diff --git a/csst_common/data_manager.py b/csst_common/data_manager.py
index 7c81004b94dbfefa63838e3ca2567b1afa053f66..79b8743102509a3968d456644c6190770e7127bb 100644
--- a/csst_common/data_manager.py
+++ b/csst_common/data_manager.py
@@ -660,7 +660,11 @@ class CsstMsDataManager:
             obstime=-1,
             limit=-1
     ):
-        """ Query Reference Catalog (RC) from DFS. """
+        """ Query Reference Catalog (RC) from DFS.
+        Ref.
+        https://gea.esac.esa.int/archive/documentation/GDR3/Gaia_archive/chap_datamodel/
+        sec_dm_main_source_catalogue/ssec_dm_gaia_source.html
+        """
         try:
             cat = self.dfs_CatApi.catalog_query(
                 catalog_name="gaia3",