diff --git a/src/main/java/com/baidu/hugegraph/util/TriFunction.java b/src/main/java/com/baidu/hugegraph/util/TriFunction.java
index 919c2c811..19723fcc7 100644
--- a/src/main/java/com/baidu/hugegraph/util/TriFunction.java
+++ b/src/main/java/com/baidu/hugegraph/util/TriFunction.java
@@ -1,5 +1,5 @@
 package com.baidu.hugegraph.util;
 
 public interface TriFunction <T1, T2, T3, R> {
-    public String apply(T1 v1, T2 v2, T3 v3);
+    public R apply(T1 v1, T2 v2, T3 v3);
 }