diff --git a/csst_mci_sim/help/demo_mci.py b/csst_mci_sim/help/demo_mci.py
new file mode 100644
index 0000000000000000000000000000000000000000..7b4d54140815f52c2614d288d27785e92638e52b
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+++ b/csst_mci_sim/help/demo_mci.py
@@ -0,0 +1,35 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+"""
+This is an example for mci simulation.
+
+@author: yan
+"""
+import os
+from csst_mci_sim import csst_mci_sim
+
+# Set the parent path where the MCI_inputdata folder is stored.
+dir_path = 'home/yan/'
+
+# Set the path to the called config file.
+configfile = os.path.join(dir_path, 'MCI_inputData/configData/mci_C10.config')
+
+# Set the path to the simulation data storage file.
+result_path = os.path.join(dir_path, 'mci_sim_result')
+
+sourcein = 'STAR'  # or EXDF or FLAT or DARK or BIAS
+
+# Specifies whether the debug mode is used. If debug=True,
+# this mode is used and the program will only simulate a few wavelength slices
+# to save time. If debug=False, the full simulation will be run.
+debug = False
+
+# set the simulaiton number. With modifications, parallel simulations
+# can be executed.
+iLoop = 1
+
+# run the main function
+# When the last parameter is yes and sourcein is LAMP,
+# the Hole simulation is executed.
+csst_mci_sim.runMCIsim(sourcein, configfile, dir_path,
+                       result_path, debug, iLoop)