diff --git a/csst_ifs_sim/csst_ifs_sim.py b/csst_ifs_sim/csst_ifs_sim.py
index 9e4dd9151064857ba358276fed9da42def300731..06af8c210eca5a55c25baf8cac2338aa0df599c6 100644
--- a/csst_ifs_sim/csst_ifs_sim.py
+++ b/csst_ifs_sim/csst_ifs_sim.py
@@ -119,6 +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
@@ -130,7 +131,6 @@ from optparse import OptionParser
 import configparser as ConfigParser
 import cmath
 from scipy import ndimage
-import galsim
 from scipy.signal import fftconvolve
 from astropy.io import fits
 import scipy.io as sio