The western Sichuan Plateau is part of the southeastern margin of the Qinghai-Tibet Plateau and the Hengduan Mountains. The ground level is 4000-4500 meters above sea level. It is divided into two parts: the northwestern plateau and the western Sichuan. The dividing line between the western Sichuan Plateau and the Chengdu Plain is the mountain range of Ya`an in the present, and the west of the mountain is the western Sichuan Plateau.