diff --git a/csst_ifs_sim/csst_ifs_sim.py b/csst_ifs_sim/csst_ifs_sim.py
index 06af8c210eca5a55c25baf8cac2338aa0df599c6..0631511f9c04195055df50a426810f12c7c3bb79 100644
--- a/csst_ifs_sim/csst_ifs_sim.py
+++ b/csst_ifs_sim/csst_ifs_sim.py
@@ -119,7 +119,7 @@ Contact Information: zhaojunyan@shao.ac.cn
 """
 import sys
 import os
-import galsim
+
 from scipy.interpolate import interp1d
 import astropy.coordinates as coord
 import ctypes
@@ -146,7 +146,7 @@ from scipy.integrate import simps
 from astropy.utils.iers import conf
 conf.auto_max_age = None
 
-
+import galsim
 ###import julian