diff --git a/docs/source/c8_changes.rst b/docs/source/c8_changes.rst
index 54a31d96c52ee922ec4fc8af46e89daedab417e3..22bc49bbee9b1ec614dbf6482ac35a7597d8ecae 100644
--- a/docs/source/c8_changes.rst
+++ b/docs/source/c8_changes.rst
@@ -28,19 +28,54 @@ Change list
 
         .. code-block:: python
 
+            import os.path
+
+            import numpy as np
+            from astropy.io import fits
+            from astropy import table
             from csst_common.status import CsstStatus, CsstResult
 
-            def base_distortion(input_file, output_file, rc="/path/to/gaia_dr3.fits", **kwargs): -> CsstResult:
-                """ your docstring here """
-                # do your calculation
-                process(input_file, output_fle)
+
+            def read_data(file_path: str = "/path/to/data") -> np.ndarray:
+                return fits.getdata(file_path)
+
+
+            def _do_step_one(data: np.ndarray) -> np.ndarray:
+                reduced_data = np.fliplr(data)
+                return reduced_data
+
+
+            def _do_step_two(data: np.ndarray) -> np.ndarray:
+                reduced_data = np.flipud(data)
+                return reduced_data
+
+
+            def _do_step_three(data: np.ndarray, rc="/path/to/catalog") -> np.ndarray:
+                trc = table.Table.read(rc)
+                return data + np.mean(trc["ra"]) + np.mean(trc["dec"])
+
+
+            def base_distortion(
+                input_file, output_file, rc: str = "/path/to/gaia_dr3.fits", **kwargs
+            ) -> CsstResult:
+                """your docstring here"""
+                # read data
+                data = read_data(input_file)
+                # do your algorithm
+                data = _do_step_one(data)
+                data = _do_step_two(data)
+                data = _do_step_three(data, rc=rc)
+                # write results
+                hl = fits.HDUList(fits.PrimaryHDU(data=data))
+                hl.writeto(output_file, overwrite=True)
+                assert os.path.exists(output_file)
                 # construct CsstResult
                 result = CsstResult(
-                    status=CsstStatus.PERFECT,
-                    file_list=[output_file, "an additional output file"]
+                    status=CsstStatus.PERFECT, file_list=[output_file, "an additional output file"]
                 )
                 return result
 
+
 导入模块
 ---------