diff --git a/chat/core/src/main/java/com/tencent/supersonic/chat/core/knowledge/MultiCustomDictionary.java b/chat/core/src/main/java/com/tencent/supersonic/chat/core/knowledge/MultiCustomDictionary.java
index 1240e7299..cda2fdde1 100644
--- a/chat/core/src/main/java/com/tencent/supersonic/chat/core/knowledge/MultiCustomDictionary.java
+++ b/chat/core/src/main/java/com/tencent/supersonic/chat/core/knowledge/MultiCustomDictionary.java
@@ -353,7 +353,7 @@ public class MultiCustomDictionary extends DynamicCustomDictionary {
 
     }
 
-    public boolean insert(String word, String natureWithFrequency) {
+    public synchronized boolean insert(String word, String natureWithFrequency) {
         if (word == null) {
             return false;
         } else {