diff --git a/csst_mci_sim/csst_mci_sim.py b/csst_mci_sim/csst_mci_sim.py
index d6a721899cce0a0a68f3dfdf9f7b46d5203cd68f..5fd3bb1f3edf8541b77410e035ecc4516de8e586 100644
--- a/csst_mci_sim/csst_mci_sim.py
+++ b/csst_mci_sim/csst_mci_sim.py
@@ -1258,7 +1258,7 @@ class MCIsimulator():
         self.information['I_filters']=["z",      "y",    "F815N", "CBI",  "F925N", "F960M",  "F968N",  "F845M" ,"F850LP" ,"F814W"]
         
         #### load telescope efficiency data
-        self.tel_eff=np.load(self.information['dir_path']+('MCI_inputData/tel_eff/tel_eff.npy',allow_pickle=True).item()
+        self.tel_eff=np.load(self.information['dir_path']+'MCI_inputData/tel_eff/tel_eff.npy',allow_pickle=True).item()
         
         #### load MCI filter data
         self.filterP=np.load(self.information['dir_path']+'MCI_inputData/MCI_filters/mci_filterPWTC.npy',allow_pickle=True).item()