The Amushan Formation has been widely used since its founding. It was once synonymous with the Upper Carboniferous of Inner Mongolia geosyncline zone in the last century. With the improvement of geological research, the subdivision of tectonic units, stratigraphic regionalization and other changes have also occurred. Based on a comprehensive study of regional data, the authors hold that the Amushan Formation is the deposition production of the northern Late Paleozoic continental margin of North China plate, and the outcropped areas are restricted to south of Solon- Siramulen River fault. It was formed during the upper Carboniferous-Lower Permian period (C2-P1), and its limestone layer is rich in fusulinids, corals and other fossils. The Amushan Formation and the Sanmianjing Formation are products of different stratigraphic subdivisions in the same stratigraphic region.