diff --git a/csst_common/data_manager.py b/csst_common/data_manager.py
index 74096f18c1ff91f225a4dd34431e8d030acea699..e54da2d8b43d9999b4a8f94467d1a2af034cc85b 100644
--- a/csst_common/data_manager.py
+++ b/csst_common/data_manager.py
@@ -580,16 +580,17 @@ class CsstMsDataManager:
 
     def get_shutter(self, detector=6):
         """ get flat data """
-        if self.custom_flat is None:
-            return os.path.join(
-                self.path_aux,
-                "C6.2_ref_mbi",
-                "CSST_MSC_MS_SHUTTER_{:02d}_{:04d}.fits".format(
-                    detector, 1 if self.ref_version is None else self.ref_version
-                )
+        fp = os.path.join(
+            self.path_aux,
+            "C6.2_ref_mbi",
+            "CSST_MSC_MS_SHUTTER_{:02d}_{:04d}.fits".format(
+                detector, 1 if self.ref_version is None else self.ref_version
             )
+        )
+        if not os.path.exists(fp):
+            raise FileNotFoundError(fp)
         else:
-            return self.custom_flat.format("flat", detector)
+            return fp
 
     def get_axeconf(self):
         return os.path.join(self.path_aux, "axeconf")  # "/home/csstpipeline/L1Pipeline/aux/axeconf"