diff --git a/mindspore/python/mindspore/rewrite/api/node.py b/mindspore/python/mindspore/rewrite/api/node.py
index 8732a2c73ff..6936f38e44e 100644
--- a/mindspore/python/mindspore/rewrite/api/node.py
+++ b/mindspore/python/mindspore/rewrite/api/node.py
@@ -88,8 +88,8 @@ class Node:
             RuntimeError: If value of kwarg in `kwargs` is not a `NamingValue`-`ScopedValue` or a
                 `CustomObjValue`-`ScopedValue`.
         """
-        return Node(NodeImpl.create_call_buildin_op(cell, None, targets, ScopedValue.create_naming_value(name, "self"),
-                                                    args, kwargs, name))
+        return Node(NodeImpl.create_call_op(cell, None, targets, ScopedValue.create_naming_value(name, "self"),
+                                            args, kwargs, name))
 
     def get_prev(self) -> 'Node':
         """
diff --git a/mindspore/python/mindspore/rewrite/api/symbol_tree.py b/mindspore/python/mindspore/rewrite/api/symbol_tree.py
index 3e998f3b646..b428d446a63 100644
--- a/mindspore/python/mindspore/rewrite/api/symbol_tree.py
+++ b/mindspore/python/mindspore/rewrite/api/symbol_tree.py
@@ -51,14 +51,15 @@ class SymbolTree:
         """
         return self._symbol_tree
 
-    def nodes(self) -> {}:
+    def nodes(self):
         """
         Get all nodes of corresponding network.
 
         Returns:
             A dict mapping from name of node to node.
         """
-        return [Node(node_impl) for node_impl in self._symbol_tree.nodes(unfold_subtree=False)]
+        for node in self._symbol_tree.nodes():
+            yield Node(node)
 
     def get_node(self, node_name: str) -> Optional[Node]:
         """
diff --git a/mindspore/python/mindspore/rewrite/api/tree_node_helper.py b/mindspore/python/mindspore/rewrite/api/tree_node_helper.py
index 10a66757206..b3a1d38c0f3 100644
--- a/mindspore/python/mindspore/rewrite/api/tree_node_helper.py
+++ b/mindspore/python/mindspore/rewrite/api/tree_node_helper.py
@@ -19,7 +19,6 @@ from .symbol_tree import SymbolTree
 from .node import Node
 from .node_type import NodeType
 from ..symbol_tree import SymbolTree as SymbolTreeImpl
-from ..node import TreeNode
 
 
 class TreeNodeHelper:
@@ -47,7 +46,6 @@ class TreeNodeHelper:
 
         if node.get_node_type() == NodeType.Tree:
             node_impl = node.get_handler()
-            assert isinstance(node_impl, TreeNode)
             subtree: SymbolTreeImpl = node_impl.symbol_tree
             if subtree is None:
                 return None
diff --git a/mindspore/python/mindspore/rewrite/namespace.py b/mindspore/python/mindspore/rewrite/namespace.py
new file mode 100644
index 00000000000..7baa5d2a224
--- /dev/null
+++ b/mindspore/python/mindspore/rewrite/namespace.py
@@ -0,0 +1,31 @@
+# Copyright 2022 Huawei Technologies Co., Ltd
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+# ============================================================================
+"""Define the namespace of MindSpore op definition."""
+from .._extends.parse.namespace import CellNamespace
+
+
+_ms_common_ns = CellNamespace('mindspore.common')
+_ms_nn_ns = CellNamespace('mindspore.nn')
+_ms_ops_ns = CellNamespace('mindspore.ops')
+
+
+def is_subtree(cls_name):
+    """Determine whether 'cls_name' is a subtree."""
+    if cls_name == "SequentialCell":
+        return True
+    if cls_name in _ms_common_ns or cls_name in _ms_nn_ns or cls_name in _ms_ops_ns:
+        return False
+
+    return True
diff --git a/mindspore/python/mindspore/rewrite/node.py b/mindspore/python/mindspore/rewrite/node.py
index cb38f4b88d7..777933ff703 100644
--- a/mindspore/python/mindspore/rewrite/node.py
+++ b/mindspore/python/mindspore/rewrite/node.py
@@ -23,6 +23,8 @@ from mindspore import log as logger
 from .ast_helpers import AstModifier
 from .api.scoped_value import ScopedValue, ValueType
 from .api.node_type import NodeType
+from .namespace import is_subtree
+from .ast_helpers.ast_replacer import AstReplacer
 
 PASS_THROUGH_METHOD = ScopedValue.create_naming_value("PassThrough")
 
@@ -223,6 +225,41 @@ class Node:
         return cls(NodeType.Output, ast_node, None, ScopedValue.create_naming_value("return"), real_return_values, {},
                    name, None)
 
+    @staticmethod
+    def create_call_op(op: Union[Cell, Primitive], ast_node: Optional[ast.AST],
+                       targets: [Union[ScopedValue, str]], func: Union[ScopedValue, str],
+                       args: [ScopedValue] = None, kwargs: {str: ScopedValue}=None, name: str = ""):
+        """
+        Static method of Node. Instantiate an instance of node whose type is `CallCell` or `CallPrimitive`.
+        If op is custom defined, it is treated by TreeNode.
+        A `CallCell` node represents an invoking to cell-op.
+        A `CallPrimitive` node represents an invoking to primitive-op.
+
+        Args:
+            op (Union[Cell, Primitive]): An instance of `Cell` or `Primitive` corresponding to this node.
+            ast_node ([ast.AST, optional]): An instance of ast.AST represents corresponding node in ast.
+            targets (list[ScopedValue]): A list of instance of `ScopedValue`. See detail in docstring of Node class.
+            func ([ScopedValue, optional]): An instance of `ScopedValue`. See detail in docstring of Node class.
+            args (list[ScopedValue]): A list of instance of `ScopedValue`. See detail in docstring of Node class.
+            kwargs (dict{str: ScopedValue}): A list of instance of `ScopedValue`. See detail in docstring of `Node`
+                class.
+            name (str): A string represents name of node. Name of node will be unique when inserted into `SymbolTree`.
+                Name of node also used as field name in network class.
+        """
+        cls_name = type(op).__name__
+
+        if is_subtree(cls_name):
+            from .symbol_tree_builder import SymbolTreeBuilder
+            stb = SymbolTreeBuilder(op)
+            stree = stb.build()
+            replacer = AstReplacer(stree.get_class_ast())
+            replacer.replace_all(stree.get_ori_cls_name(), stree.get_opt_cls_name())
+            return TreeNode.create_tree_node(stree, None, targets, ScopedValue.create_naming_value(name, "self"),
+                                             args, kwargs, name, op)
+
+        return Node.create_call_buildin_op(op, None, targets, ScopedValue.create_naming_value(name, "self"),
+                                           args, kwargs, name)
+
     @staticmethod
     def _get_construct_arg_names(parameters):
         """
@@ -440,6 +477,10 @@ class Node:
         """
         return self._prev
 
+    def set_prev(self, prev):
+        """Set previous node of current node in source code order. """
+        self._prev = prev
+
     def get_next(self) -> 'Node':
         """
         Get next node of current node in source code order.
@@ -449,6 +490,10 @@ class Node:
         """
         return self._next
 
+    def set_next(self, _next):
+        """Set next node of current node in source code order."""
+        self._next = _next
+
     def has_same_ast(self, node: Union['Node', ast.AST]) -> bool:
         """
         Check if other node holds same ast node with self.
@@ -460,7 +505,7 @@ class Node:
             A bool.
         """
         if isinstance(node, Node):
-            return self.has_same_ast(node._ast_node)
+            return self.has_same_ast(node.get_ast())
         if isinstance(node, ast.AST):
             return id(self._ast_node) == id(node)
         return False
@@ -570,7 +615,8 @@ class Node:
             keyword_map_index[keyword_ast.arg] = index
         for keyword_index in range(self._kwargs_num):
             key = self._normalized_args_keys[keyword_index + self._args_num]
-            AstModifier.update_arg_value(self._normalized_args.get(key), keywords_ast[keyword_map_index[key]].value)
+            AstModifier.update_arg_value(self._normalized_args.get(key),
+                                         keywords_ast[keyword_map_index.get(key)].value)
 
     def _sync_call_method_args_to_ast(self):
         """Sync args of ast.Cell of ast.Assign from self._normalized_args when NodeType is CallMethod."""
@@ -646,9 +692,9 @@ class Node:
         origin_prev: Optional[Node] = self._prev
         origin_next: Optional[Node] = self._next
         if origin_prev is not None:
-            origin_prev._next = origin_next
+            origin_prev.set_next(origin_next)
         if origin_next is not None:
-            origin_next._prev = origin_prev
+            origin_next.set_prev(origin_prev)
         self._prev = None
         self._next = None
 
@@ -662,9 +708,9 @@ class Node:
         node.isolate()
         origin_prev: Optional[Node] = self._prev
         if origin_prev is not None:
-            origin_prev._next = node
-        node._prev = origin_prev
-        node._next = self
+            origin_prev.set_next(node)
+        node.set_prev(origin_prev)
+        node.set_next(self)
         self._prev = node
 
     def insert_after(self, node: 'Node'):
@@ -677,10 +723,10 @@ class Node:
         node.isolate()
         origin_next: Optional[Node] = self._next
         self._next = node
-        node._prev = self
-        node._next = origin_next
+        node.set_prev(self)
+        node.set_next(origin_next)
         if origin_next is not None:
-            origin_next._prev = node
+            origin_next.set_prev(node)
 
     def get_inputs(self) -> ['Node']:
         """
@@ -850,12 +896,12 @@ class Node:
         if arg_idx >= self._args_num or arg_idx < 0:
             raise RuntimeError("arg_idx out of range: ", arg_idx)
         if out_idx is None:
-            if len(node._targets) != 1:
+            if len(node.get_targets()) != 1:
                 raise RuntimeError("node should has one output when out_idx is not provided")
             out_idx = 0
-        if out_idx >= len(node._targets):
+        if out_idx >= len(node.get_targets()):
             raise RuntimeError("out_idx out of range: ", out_idx)
-        new_arg = node._targets[out_idx]
+        new_arg = node.get_targets()[out_idx]
         self._normalized_args[self._normalized_args_keys[arg_idx]] = new_arg
         self._sync_arg()
 
diff --git a/mindspore/python/mindspore/rewrite/node_visitor.py b/mindspore/python/mindspore/rewrite/node_visitor.py
new file mode 100644
index 00000000000..0caa11a361c
--- /dev/null
+++ b/mindspore/python/mindspore/rewrite/node_visitor.py
@@ -0,0 +1,44 @@
+# Copyright 2022 Huawei Technologies Co., Ltd
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+# ============================================================================
+"""Visit nods of SymbolTree."""
+
+
+class NodeVisitor:
+    """Iterator class to access SymbolTree nodes"""
+    def __init__(self, stree):
+        self._stree = stree
+        self._nodes = []
+        self._index = 0
+
+    def __iter__(self):
+        self._nodes = list(self._stree.get_nodes_dict().values())
+        self._index = 0
+        return self
+
+    def __next__(self):
+        if self._index < len(self._nodes):
+            node = self._nodes[self._index]
+            self._index += 1
+            return node
+
+        raise StopIteration
+
+    def append_node(self, node):
+        """append new node to iterator"""
+        self._nodes.append(node)
+
+    def remove_node(self, node):
+        """remove node of iterator"""
+        self._nodes.remove(node)
diff --git a/mindspore/python/mindspore/rewrite/parsers/assign_parser.py b/mindspore/python/mindspore/rewrite/parsers/assign_parser.py
index c6606ab6171..afb33c1eee4 100644
--- a/mindspore/python/mindspore/rewrite/parsers/assign_parser.py
+++ b/mindspore/python/mindspore/rewrite/parsers/assign_parser.py
@@ -186,7 +186,6 @@ class AssignParser(Parser):
         return results
 
     def _is_subtree_cell(self, cell: Cell) -> bool:
-        assert isinstance(cell, Cell)
         return not type(cell).__name__ in self._cell_namespce
 
     @staticmethod
@@ -353,7 +352,6 @@ class AssignParser(Parser):
                 # self._subnet = SubNet1(global_vars.get("subnet_args"))
                 # so a change in sub-network should also be identified as a change in main-network.
                 # so main-network should observe sub-network
-                new_stree.reg_observer(stree)
                 replacer = AstReplacer(new_stree.get_class_ast())
                 replacer.replace_all(new_stree.get_ori_cls_name(), new_stree.get_opt_cls_name())
                 return TreeNode(new_stree, father_ast_node, targets, func, call_args, call_kwargs, func_name,
diff --git a/mindspore/python/mindspore/rewrite/parsers/class_def_parser.py b/mindspore/python/mindspore/rewrite/parsers/class_def_parser.py
index 15d4737d284..e76601d4402 100644
--- a/mindspore/python/mindspore/rewrite/parsers/class_def_parser.py
+++ b/mindspore/python/mindspore/rewrite/parsers/class_def_parser.py
@@ -114,7 +114,6 @@ class ClassDefParser(Parser):
 
     def _is_subtree_field(self, ori_net, field) -> bool:
         op = getattr(ori_net, field)
-        assert op is not None
         return not type(op).__name__ in self._cell_namespace
 
     def _process_init_func_ast(self, stree: SymbolTree, init_ast: ast.FunctionDef):
diff --git a/mindspore/python/mindspore/rewrite/symbol_tree.py b/mindspore/python/mindspore/rewrite/symbol_tree.py
index 486210b3838..f63679c9a62 100644
--- a/mindspore/python/mindspore/rewrite/symbol_tree.py
+++ b/mindspore/python/mindspore/rewrite/symbol_tree.py
@@ -32,6 +32,7 @@ from .namer import TargetNamer, NodeNamer, ClassNamer
 from .common.observer import Observer
 from .common.observable import Observable
 from .common.event import Event
+from .node_visitor import NodeVisitor
 
 
 class Position:
@@ -113,6 +114,7 @@ class SymbolTree(Observer, Observable):
         self._return: Optional[Node] = None
 
         self._modified = False
+        self._node_visitor = None
 
     def finish_build(self):
         self.add_event(Event.TopologicalChangeEvent)
@@ -258,25 +260,27 @@ class SymbolTree(Observer, Observable):
             raise RuntimeError("Key of global_vars duplicated:", key)
         self._global_vars[key] = value
 
-    def nodes(self, unfold_subtree=False):
+    def get_nodes_dict(self):
+        """Get dict of nodes"""
+        return self._nodes
+
+    def nodes(self):
         """
         Getter of nodes if current SymbolTree.
 
-        Args:
-            unfold_subtree (bool): Need to iterate into sub-symbol-tree recursively.
-
         Returns:
             A list of instance of Nodes.
         """
-        if unfold_subtree:
-            nodes = []
-            for _, v in self._nodes.items():
-                if isinstance(v, TreeNode):
-                    nodes.extend(v.symbol_tree.nodes(unfold_subtree))
-                else:
-                    nodes.append(v)
-            return nodes
-        return self._nodes.values()
+        if self._node_visitor is None:
+            self._node_visitor = NodeVisitor(self)
+        it = iter(self._node_visitor)
+
+        while True:
+            try:
+                n = next(it)
+                yield n
+            except StopIteration:
+                return None
 
     def get_node(self, node_name: str) -> Optional[Node]:
         """
@@ -431,19 +435,44 @@ class SymbolTree(Observer, Observable):
         # _unique_targets must called after _update_args_for_unique and _update_kwargs_for_unique
         self._unique_targets(node)
         self._insert_node(position, node)
+        if isinstance(node, TreeNode):
+            node.symbol_tree.reg_observer(self)
+        if self._node_visitor:
+            self._node_visitor.append_node(node)
         # update init-function-ast and construct-function-ast
         if insert_to_ast:
             node.set_func(ScopedValue.create_naming_value(node_name, "self"))
-            node_ast = node.get_ast()
-            if not isinstance(node_ast, ast.Assign):
-                raise RuntimeError("Only support insert cell op now")
-            AstModifier.insert_assign_to_function(self._init_func_ast,
-                                                  targets=[ScopedValue(ValueType.NamingValue, "self", node_name)],
-                                                  expr=ScopedValue(ValueType.NamingValue, "global_vars", "get"),
-                                                  args=[ScopedValue(ValueType.StringValue, "", node_name)])
-            AstModifier.insert_assign_ast_to_function(self._root_ast, node_ast,
-                                                      None if position is None else position.node.get_ast(),
-                                                      position.before_node)
+            if isinstance(node, TreeNode):
+                global_vars_key = node.get_name() + "_args"
+                self.add_global_vars(global_vars_key, node.symbol_tree.get_global_vars())
+                args_call = AstModifier.create_call(ScopedValue.create_naming_value("get", "global_vars"),
+                                                    [ScopedValue.create_variable_value(global_vars_key)])
+                value = ast.Call(func=ast.Name(node.symbol_tree.get_opt_cls_name(), ast.Store(), lineno=0,
+                                               col_offset=0), args=[args_call], keywords=[], lineno=0, col_offset=0)
+
+                ast_target = ast.Name("self." + node.get_name(), ast.Store(), lineno=0, col_offset=0)
+                assign = ast.Assign(targets=[ast_target], value=value, lineno=0, col_offset=0)
+                AstModifier.insert_assign_ast_to_function(self._init_func_ast, assign)
+
+                assign_construct = AstModifier.create_call_assign(node.get_targets(), ScopedValue.create_naming_value
+                                                                  (node.get_name(), "self"), node.get_args(), {})
+                AstModifier.insert_assign_ast_to_function(self._root_ast, assign_construct,
+                                                          None if position is None else position.node.get_ast(),
+                                                          position.before_node)
+                sub_stree: SymbolTree = node.symbol_tree
+                from .symbol_tree_builder import SymbolTreeBuilder
+                SymbolTreeBuilder.merge_module_of_subtree(self, sub_stree)
+            else:
+                node_ast = node.get_ast()
+                if not isinstance(node_ast, ast.Assign):
+                    raise RuntimeError("Only support insert cell op now")
+                AstModifier.insert_assign_to_function(self._init_func_ast,
+                                                      targets=[ScopedValue(ValueType.NamingValue, "self", node_name)],
+                                                      expr=ScopedValue(ValueType.NamingValue, "global_vars", "get"),
+                                                      args=[ScopedValue(ValueType.StringValue, "", node_name)])
+                AstModifier.insert_assign_ast_to_function(self._root_ast, node_ast,
+                                                          None if position is None else position.node.get_ast(),
+                                                          position.before_node)
             self._global_vars[node_name] = node.get_instance()
         return node
 
@@ -595,6 +624,8 @@ class SymbolTree(Observer, Observable):
                 value.isolate()
                 break
         self._topo_mgr.on_erase_node(node)
+        if self._node_visitor:
+            self._node_visitor.remove_node(node)
         return node
 
     def _insert_tree(self, position: Position, root: Node, insert_to_ast: bool = True) -> Node:
diff --git a/mindspore/python/mindspore/rewrite/symbol_tree_builder.py b/mindspore/python/mindspore/rewrite/symbol_tree_builder.py
index 33e78002c82..a29f249b9e9 100644
--- a/mindspore/python/mindspore/rewrite/symbol_tree_builder.py
+++ b/mindspore/python/mindspore/rewrite/symbol_tree_builder.py
@@ -44,6 +44,22 @@ class SymbolTreeBuilder:
         self._ast_root: ast.Module = ast.parse(network_str)
         self._root_tree: Optional[SymbolTree] = None
 
+    @staticmethod
+    def merge_module_of_subtree(main_tree: SymbolTree, sub_stree: SymbolTree):
+        """
+        Merge ast.Module of sub-network into ast.Module of main-network.
+
+        1. Merge imports of ast.Module.
+        2. Merge classes of ast.Module.
+        3. Use merged ast.Module as module of main-network and sub-network.
+        """
+
+        father_mod = main_tree.get_module_ast()
+        sub_mod = sub_stree.get_module_ast()
+        SymbolTreeBuilder._merge_import_of_module(father_mod, sub_mod)
+        SymbolTreeBuilder._merge_class_of_module(father_mod, sub_mod)
+        sub_stree.set_module_ast(father_mod)
+
     @staticmethod
     def _ast_transform(ast_root: ast.AST) -> ast.AST:
         """
@@ -80,7 +96,6 @@ class SymbolTreeBuilder:
         main_mod_finder = AstFinder(main_mod)
         imports_in_sub = copy(sub_mod_finder.find_all((ast.Import, ast.ImportFrom)))
         imports_in_main = copy(main_mod_finder.find_all((ast.Import, ast.ImportFrom)))
-        assert imports_in_main
         first_import = imports_in_main[0]
         for clazz in imports_in_sub:
             AstModifier.insert_sub_ast(main_mod, clazz, first_import, True)
@@ -103,12 +118,11 @@ class SymbolTreeBuilder:
         main_mod_finder = AstFinder(main_mod)
         classes_in_sub = copy(sub_mod_finder.find_all(ast.ClassDef))
         classes_in_main = copy(main_mod_finder.find_all(ast.ClassDef))
-        assert classes_in_main
         first_class = classes_in_main[0]
         for clazz in classes_in_sub:
             AstModifier.insert_class_into_module(main_mod, clazz, first_class, True)
 
-    def _merge_module_of_subtree(self):
+    def _merge_module_of_subtrees(self):
         """
         Merge ast.Module of all sub-networks into ast.Module of main-network.
 
@@ -117,13 +131,9 @@ class SymbolTreeBuilder:
         3. Use merged ast.Module as module of main-network and sub-network.
         """
 
-        father_mod = self._root_tree.get_module_ast()
         for node in self._root_tree.nodes():
             if isinstance(node, TreeNode):
-                sub_stree: SymbolTree = node.symbol_tree
-                SymbolTreeBuilder._merge_import_of_module(father_mod, sub_stree.get_module_ast())
-                SymbolTreeBuilder._merge_class_of_module(father_mod, sub_stree.get_module_ast())
-                sub_stree.set_module_ast(father_mod)
+                SymbolTreeBuilder.merge_module_of_subtree(self._root_tree, node.symbol_tree)
 
     def _reduce_redundant_import(self):
         """
@@ -140,7 +150,6 @@ class SymbolTreeBuilder:
             if isinstance(body, ast.Import):
                 names = body.names
                 for name in names:
-                    assert isinstance(name, ast.alias)
                     import_hash = hash((name.name, name.asname))
                     if import_hash in exist_import:
                         continue
@@ -150,7 +159,6 @@ class SymbolTreeBuilder:
                 import_module = body.module
                 names = body.names
                 for name in names:
-                    assert isinstance(name, ast.alias)
                     import_hash = hash((import_module, name.name, name.asname))
                     if import_hash in exist_import_from:
                         continue
@@ -182,7 +190,7 @@ class SymbolTreeBuilder:
         self._root_tree: SymbolTree = SymbolTree(self._origin_net, self._ast_root)
         parser: Parser = ParserRegister.instance().get_parser(ast.Module)
         parser.process(self._root_tree, self._ast_root)
-        self._merge_module_of_subtree()
+        self._merge_module_of_subtrees()
         self._reduce_redundant_import()
         ast.fix_missing_locations(self._root_tree.get_module_ast())
         self._root_tree.finish_build()
diff --git a/tests/ut/python/rewrite/test_multiple_targets.py b/tests/ut/python/rewrite/test_multiple_targets.py
index daaf250a537..3236d08fe03 100644
--- a/tests/ut/python/rewrite/test_multiple_targets.py
+++ b/tests/ut/python/rewrite/test_multiple_targets.py
@@ -15,6 +15,7 @@
 from mindspore.nn import Cell, Conv2d
 from mindspore.rewrite import SymbolTree
 from mindspore.ops import operations as P
+from .utils import get_node_by_index
 
 
 class SubNet(Cell):
@@ -56,7 +57,8 @@ def test_multi_targets():
     """
     test_cls = NetMultiTargets()
     stree = SymbolTree.create(test_cls)
-    node = stree.nodes()[2]
+    node = get_node_by_index(stree, 2)
+    assert node is not None
     targets = node.get_targets()
     assert targets[0].value == 'c1'
     assert targets[1].value == 'c2'
diff --git a/tests/ut/python/rewrite/test_net_simple.py b/tests/ut/python/rewrite/test_net_simple.py
index 8a42f65a7f3..c6c6c2cc514 100644
--- a/tests/ut/python/rewrite/test_net_simple.py
+++ b/tests/ut/python/rewrite/test_net_simple.py
@@ -121,7 +121,6 @@ def erase_node_x_11(stree: SymbolTree):
 
 def transform(stree: SymbolTree):
     add_conv_before_flatten(stree)
-    add_my_cell_after_x_12(stree)
     erase_node_x_11(stree)
 
 
diff --git a/tests/ut/python/rewrite/test_pattern_engine.py b/tests/ut/python/rewrite/test_pattern_engine.py
index 73630d12208..8216e09302e 100644
--- a/tests/ut/python/rewrite/test_pattern_engine.py
+++ b/tests/ut/python/rewrite/test_pattern_engine.py
@@ -19,6 +19,7 @@ from mindspore.nn import Cell, Conv2d, BatchNorm2d, ReLU
 from mindspore.ops import Add, AddN
 from mindspore.rewrite import ScopedValue, Node, SymbolTree
 from mindspore.rewrite import PatternEngine, PatternNode, Replacement, VarNode
+from .utils import get_symbol_tree_nodes_count
 
 
 def test_tree_pattern_match():
@@ -92,13 +93,13 @@ def test_one_to_one_pattern():
     assert bn is not None
     assert relu1 is not None
     assert len(construct_ast.body) == 6
-    assert len(stree.nodes()) == 7
+    assert get_symbol_tree_nodes_count(stree) == 7
 
     bn_replace = BnReplace()
     bn_replace.apply(stree)
 
     assert len(construct_ast.body) == 6
-    assert len(stree.nodes()) == 7
+    assert get_symbol_tree_nodes_count(stree) == 7
     conv = stree.get_node("conv")
     bn = stree.get_node("bn")
     relu1 = stree.get_node("relu1")
@@ -167,13 +168,13 @@ def test_one_to_multi_chain_pattern():
     assert bn is not None
     assert relu1 is not None
     assert len(construct_ast.body) == 6
-    assert len(stree.nodes()) == 7
+    assert get_symbol_tree_nodes_count(stree) == 7
 
     bn_replace = BnReplace()
     bn_replace.apply(stree)
 
     assert len(construct_ast.body) == 7
-    assert len(stree.nodes()) == 8
+    assert get_symbol_tree_nodes_count(stree) == 8
     conv = stree.get_node("conv")
     bn = stree.get_node("bn")
     relu1 = stree.get_node("relu1")
@@ -296,13 +297,13 @@ def test_tree_pattern():
     assert relu2 is not None
     construct_ast: ast.FunctionDef = getattr(stree.get_handler(), "_root_ast")
     assert len(construct_ast.body) == 8
-    assert len(stree.nodes()) == 9
+    assert get_symbol_tree_nodes_count(stree) == 9
 
     add_relu_pattern = AddReluPattern()
     add_relu_pattern.apply(stree)
 
     assert len(construct_ast.body) == 10
-    assert len(stree.nodes()) == 11
+    assert get_symbol_tree_nodes_count(stree) == 11
     conv1 = stree.get_node("conv1")
     conv2 = stree.get_node("conv2")
     add = stree.get_node("add")
@@ -481,13 +482,13 @@ def test_multi_input_to_multi_pattern_tree_pattern():
     assert relu is not None
     construct_ast: ast.FunctionDef = getattr(stree.get_handler(), "_root_ast")
     assert len(construct_ast.body) == 6
-    assert len(stree.nodes()) == 9
+    assert get_symbol_tree_nodes_count(stree) == 9
 
     multi_input_pattern = MultiInputPattern()
     multi_input_pattern.apply(stree)
 
     assert len(construct_ast.body) == 4
-    assert len(stree.nodes()) == 7
+    assert get_symbol_tree_nodes_count(stree) == 7
     conv1 = stree.get_node("conv1")
     conv2 = stree.get_node("conv2")
     add1 = stree.get_node("add1")
@@ -598,13 +599,13 @@ def test_one_input_to_multi_pattern_tree_pattern():
     assert relu is not None
     construct_ast: ast.FunctionDef = getattr(stree.get_handler(), "_root_ast")
     assert len(construct_ast.body) == 6
-    assert len(stree.nodes()) == 7
+    assert get_symbol_tree_nodes_count(stree) == 7
 
     multi_input_pattern = MultiInputPattern()
     multi_input_pattern.apply(stree)
 
     assert len(construct_ast.body) == 4
-    assert len(stree.nodes()) == 5
+    assert get_symbol_tree_nodes_count(stree) == 5
     conv1 = stree.get_node("conv1")
     conv2 = stree.get_node("conv2")
     add1 = stree.get_node("add1")
diff --git a/tests/ut/python/rewrite/test_subtree_net.py b/tests/ut/python/rewrite/test_subtree_net.py
index 98318afa050..85d7c49871a 100644
--- a/tests/ut/python/rewrite/test_subtree_net.py
+++ b/tests/ut/python/rewrite/test_subtree_net.py
@@ -100,10 +100,52 @@ def erase_relu_in_conv2(stree: SymbolTree):
             break
 
 
+def inset_subtree(stree: SymbolTree):
+    for node in stree.nodes():
+        if node.get_name() == "conv2":
+            position = stree.before(node)
+            subtree = SubNet()
+            new_node = Node.create_call_cell(subtree, targets=[ScopedValue.create_naming_value('x')], name='conv',
+                                             args=[ScopedValue.create_naming_value('x')], kwargs={})
+            stree.insert(position, new_node)
+            break
+
+
+def inset_subtree2(stree: SymbolTree):
+    for node in stree.nodes():
+        if node.get_name() == "conv2":
+            position = stree.before(node)
+            subtree = SubNet()
+            new_node = Node.create_call_cell(subtree, targets=[ScopedValue.create_naming_value('x')], name='conv11',
+                                             args=[ScopedValue.create_naming_value('x')], kwargs={})
+            stree.insert(position, new_node)
+            break
+
+
+def add_relu_in_conv11(stree: SymbolTree):
+    for node in stree.nodes():
+        if node.get_node_type() != NodeType.Tree:
+            continue
+        if node.get_name() == "conv11":
+            _stree: SymbolTree = TreeNodeHelper.get_sub_tree(node)
+            for inner_node in _stree.nodes():
+                if inner_node.get_node_type() != NodeType.Output:
+                    continue
+                position = _stree.before(inner_node)
+                new_relu = nn.ReLU()
+                new_relu_node = Node.create_call_cell(new_relu, targets=['x'], name='relu1',
+                                                      args=[ScopedValue.create_naming_value('x')])
+                _stree.insert(position, new_relu_node)
+                _stree.set_output(0, new_relu_node.get_targets()[0].value)
+                break
+            break
+
+
 def transform(stree: SymbolTree):
     add_relu_in_conv1(stree)
     replace_bn_in_conv2(stree)
     erase_relu_in_conv2(stree)
+    inset_subtree(stree)
 
 
 def test_subtree_net():
@@ -115,7 +157,20 @@ def test_subtree_net():
 
     net = MainNet()
     stree = SymbolTree.create(net)
+    print(stree.get_code())
     transform(stree)
+    for node in stree.nodes():
+        print("after transform node name: ", node.get_name(), "; node type: ", node.get_node_type())
+        if node.get_node_type() != NodeType.Tree:
+            continue
+        if node.get_name() == "conv":
+            modify_stree: SymbolTree = TreeNodeHelper.get_sub_tree(node)
+            for inner_node in modify_stree.nodes():
+                print("inserted subtree node: ", inner_node.get_name())
+
+    inset_subtree2(stree)
+    add_relu_in_conv11(stree)
+
     print(stree.get_code())
     print(stree.get_handler().get_global_vars().keys())
     net_opt = stree.get_network()
diff --git a/tests/ut/python/rewrite/test_symbol_tree.py b/tests/ut/python/rewrite/test_symbol_tree.py
index 6599dd78804..a4a3efe7f5f 100644
--- a/tests/ut/python/rewrite/test_symbol_tree.py
+++ b/tests/ut/python/rewrite/test_symbol_tree.py
@@ -21,6 +21,7 @@ from mindspore.rewrite import ScopedValue, ValueType, NodeType
 from mindspore.rewrite import Node as NodeApi
 from mindspore.rewrite.symbol_tree import SymbolTree
 from mindspore.rewrite.node import Node
+from .utils import get_symbol_tree_nodes_count
 
 
 class Network(Cell):
@@ -107,7 +108,7 @@ def test_insert_node():
     consumers = getattr(getattr(stree, "_topo_mgr"), "_target_consumer")
     providers_len = len(providers)
     consumers_len = len(consumers)
-    assert len(stree.nodes()) == 7
+    assert get_symbol_tree_nodes_count(stree) == 7
     assert len(construct_ast.body) == 6
     assert len(relu1.get_targets()) == 1
     assert len(relu2.get_normalized_args().values()) == 1
@@ -120,7 +121,7 @@ def test_insert_node():
     position = stree.before(relu2)
     node = stree.insert_node(position, node)
     # check nodes size
-    assert len(stree.nodes()) == 8
+    assert get_symbol_tree_nodes_count(stree) == 8
     # check args
     assert len(relu2.get_normalized_args().values()) == 1
     assert relu1.get_targets()[0] == list(relu2.get_normalized_args().values())[0]
@@ -158,7 +159,7 @@ def test_set_node_arg():
     Expectation: Success.
     """
     stree, bn, relu1, relu2 = create_symbol_tree()
-    assert len(stree.nodes()) == 7
+    assert get_symbol_tree_nodes_count(stree) == 7
     assert len(bn.get_targets()) == 1
     bn_output = bn.get_targets()[0]
     # check bn topological order
@@ -210,7 +211,7 @@ def test_set_node_arg_by_node():
     Expectation: Success.
     """
     stree, bn, relu1, relu2 = create_symbol_tree()
-    assert len(stree.nodes()) == 7
+    assert get_symbol_tree_nodes_count(stree) == 7
     assert len(bn.get_targets()) == 1
     bn_output = bn.get_targets()[0]
     # check bn topological order
@@ -265,13 +266,13 @@ def test_erase_succeed():
     construct_ast: ast.FunctionDef = getattr(stree, "_root_ast")
     providers = getattr(getattr(stree, "_topo_mgr"), "_target_provider")
     providers_len = len(providers)
-    assert len(stree.nodes()) == 7
+    assert get_symbol_tree_nodes_count(stree) == 7
     assert len(construct_ast.body) == 6
 
     stree.set_node_arg_by_node(relu2, 0, bn)
     stree.erase_node(relu1)
 
-    assert len(stree.nodes()) == 6
+    assert get_symbol_tree_nodes_count(stree) == 6
     assert len(providers) == providers_len - 1
     assert len(construct_ast.body) == 5
 
@@ -300,13 +301,13 @@ def test_replace_one_to_one():
     stree, bn, relu1, relu2 = create_symbol_tree()
     construct_ast: ast.FunctionDef = getattr(stree, "_root_ast")
     assert len(construct_ast.body) == 6
-    assert len(stree.nodes()) == 7
+    assert get_symbol_tree_nodes_count(stree) == 7
 
     new_conv = Conv2d(16, 16, 5)
     new_conv_node = NodeApi.create_call_cell(new_conv, [ScopedValue.create_naming_value("new_conv")],
                                              bn.get_targets()).get_handler()
     new_conv_node = stree.replace(relu1, [new_conv_node])
-    assert len(stree.nodes()) == 7
+    assert get_symbol_tree_nodes_count(stree) == 7
     # check ast
     assert len(construct_ast.body) == 6
     node_ast: ast.Assign = construct_ast.body[2]
@@ -341,7 +342,7 @@ def test_replace_one_to_multi():
     stree, bn, relu1, relu2 = create_symbol_tree()
     construct_ast: ast.FunctionDef = getattr(stree, "_root_ast")
     assert len(construct_ast.body) == 6
-    assert len(stree.nodes()) == 7
+    assert get_symbol_tree_nodes_count(stree) == 7
 
     new_conv_node = NodeApi.create_call_cell(Conv2d(16, 16, 5), [ScopedValue.create_naming_value("new_conv")],
                                              bn.get_targets()).get_handler()
@@ -350,7 +351,7 @@ def test_replace_one_to_multi():
     new_relu_node = stree.replace(relu1, [new_relu_node, new_conv_node])
     new_conv_node = new_relu_node.get_inputs()[0]
 
-    assert len(stree.nodes()) == 8
+    assert get_symbol_tree_nodes_count(stree) == 8
     # check ast
     assert len(construct_ast.body) == 7
     new_conv_ast: ast.Assign = construct_ast.body[2]
diff --git a/tests/ut/python/rewrite/utils.py b/tests/ut/python/rewrite/utils.py
new file mode 100644
index 00000000000..61297253af0
--- /dev/null
+++ b/tests/ut/python/rewrite/utils.py
@@ -0,0 +1,31 @@
+# Copyright 2022 Huawei Technologies Co., Ltd
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+# ============================================================================
+
+from mindspore.rewrite.api.symbol_tree import SymbolTree
+
+
+def get_symbol_tree_nodes_count(stree: SymbolTree):
+    count = 0
+    for _ in stree.nodes():
+        count += 1
+    return count
+
+
+def get_node_by_index(stree: SymbolTree, index):
+    for i, node in enumerate(stree.nodes()):
+        if i == index:
+            return node
+
+    return None