diff --git a/src/agentscope/rag/knowledge_bank.py b/src/agentscope/rag/knowledge_bank.py
index 1579634a3..dc65a1ac8 100644
--- a/src/agentscope/rag/knowledge_bank.py
+++ b/src/agentscope/rag/knowledge_bank.py
@@ -133,7 +133,6 @@ def add_data_as_knowledge(
                 "please check your knowledge config",
             )
 
-        CustomKnowledge = None
         if "llama_index" in backend_engine:
             CustomKnowledge = LlamaIndexKnowledge
             logger.info("Using llama_index backend engine")