diff --git a/server/knowledge_base/utils.py b/server/knowledge_base/utils.py
index c3f4f62..677bb3d 100644
--- a/server/knowledge_base/utils.py
+++ b/server/knowledge_base/utils.py
@@ -3,6 +3,7 @@ from typing import List
 from server.utils import torch_gc
 from configs.model_config import KB_ROOT_PATH
 from langchain.vectorstores import FAISS
+from langchain.schema import Document
 from langchain.embeddings.huggingface import HuggingFaceEmbeddings
 from configs.model_config import (CACHED_VS_NUM, VECTOR_SEARCH_TOP_K,
                                   embedding_model_dict, EMBEDDING_MODEL, EMBEDDING_DEVICE)