diff --git a/reme_ai/summary/task/trajectory_preprocess_op.py b/reme_ai/summary/task/trajectory_preprocess_op.py
index 9ada5865..72d41431 100644
--- a/reme_ai/summary/task/trajectory_preprocess_op.py
+++ b/reme_ai/summary/task/trajectory_preprocess_op.py
@@ -1,3 +1,4 @@
+import json
 from typing import List, Dict
 
 from flowllm import C, BaseOp