[Objective] The objective of this article is to determine the best statistical unit to extract and classify the relief amplitude of Southwestern China, and then the characteristics of the amplitude structure and the classification of geomorphologic structure can be determined.[Methods] Based on ASTER GDEMv2 data and through Python module programming, the average relief amplitude in the Southwestern China and the typical experimental areas was extracted at n×n windows (n=2,3,4,…,181,182,183), and the best window area was calculated by the mean change point method.[Results] ① 2.43 km² was the optimal statistical unit for extracting amplitude relief in the study area. ② Fluctuation of terrain was moderate and low in the study area, with the relief amplitude between 200 m to 500 m having the highest proportion (38.68%), and that between 500 m to 1 000 m accounting for 23.58%. ③ As for the spatial distribution, the relief amplitude of the middle region was generally higher than that of other regions, followed by the southeast, lower in the northwest and northeast.[Conclusion] The method, computing relief amplitude with optimum statistical unit of 2.43 km², conformed to the regional terrain characteristics and balanced the various landform types.