diff --git a/hudi-flink-datasource/hudi-flink/src/main/java/org/apache/hudi/sink/bucket/BucketStreamWriteFunction.java b/hudi-flink-datasource/hudi-flink/src/main/java/org/apache/hudi/sink/bucket/BucketStreamWriteFunction.java
index 1ccfe91dbc0a9..09a78de4c8d15 100644
--- a/hudi-flink-datasource/hudi-flink/src/main/java/org/apache/hudi/sink/bucket/BucketStreamWriteFunction.java
+++ b/hudi-flink-datasource/hudi-flink/src/main/java/org/apache/hudi/sink/bucket/BucketStreamWriteFunction.java
@@ -111,7 +111,7 @@ public void processElement(I i, ProcessFunction<I, Object>.Context context, Coll
     bootstrapIndexIfNeed(partition);
     Map<Integer, String> bucketToFileId = bucketIndex.computeIfAbsent(partition, p -> new HashMap<>());
     final int bucketNum = BucketIdentifier.getBucketId(hoodieKey, indexKeyFields, this.bucketNum);
-    final String bucketId = partition + bucketNum;
+    final String bucketId = partition + "/" + bucketNum;
 
     if (incBucketIndex.contains(bucketId)) {
       location = new HoodieRecordLocation("I", bucketToFileId.get(bucketNum));