Abstract: Based on an analysis of basalt geochemical characteristics of Amushan Formation （western Ganquan Formation） of Upper Carboniferous Xiaodushan Stage-Lower Permian Zisong Stage and the basalt type，this paper deals with the rock characteristics and tectonic environment. Previous studies have already revealed the basic type of Carboniferous-Permian basin. The Zr/TiO2-Nb/Y，SiO2-TFeO/MgO and Zr-Y-Nb diagrams show that the basalt in Ejin Banner and its vicinities is mainly of the sub-alkaline tholeiite series. Chondrite-normalized REE patterns are right-oblique curves; the relatively high (La/Yb）N and low (Gd/Lu）N indicate that light rare earth elements have experienced obvious fractionation，but heavy rare earth elements have been only subjected to week fractionation，and δEu=0.87~1.11，without remarkable Eu depletion；N-MORB-normalized spider diagram shows relatively high abundances of K2O，Rb， Ba，Th and low abundances of Hf，Nb，Y. Through an analysis of Zr-Zr/Y and Ta/Hf-Th/Hf diagrams，it is considered that the basalt in the study area should be of the sub-alkaline tholeiite series occurring in the rift valley，and Ejin Banner and its vicinities entered into an intracontinental evolution period, being a rift basin by tension.