diff --git a/csst_dfs_api_cluster/msc/level1.py b/csst_dfs_api_cluster/msc/level1.py
index 6ec3823cae4758bcd76ce8658fc12b2f34cfb310..fd8db798711fdcfdb9c5a078b75ba495e7134302 100644
--- a/csst_dfs_api_cluster/msc/level1.py
+++ b/csst_dfs_api_cluster/msc/level1.py
@@ -159,6 +159,7 @@ class Level1DataApi(object):
             with open(rec.file_path, 'rb') as f:
                 while True:
                     data = f.read(UPLOAD_CHUNK_SIZE)
+                    print("read data len: %d" %(len(data),))
                     if not data:
                         break
                     yield level1_pb2.WriteLevel1Req(record = rec, data = data)