Abstract: Late Paleozoic Yingen-Ejin Banner basin characterized by stable sedimentary formation, clear lithofacies, distinct stratigraphic sequence and depositional system tract has developed a set of Carboniferous-Permian volcanic rocks, clastic rocks and carbonates. Based on an analysis of formation characteristics and lateral variation in this sedimentary basin, the authors divided preliminarily the basin into 4 II-grade sequences and 8 Ⅲ-grade sequences, and identified several depositional system tracts and sequence interface. The rising velocity of the basin sea was quick during the formation of Ⅰ, Ⅳ, Ⅵ, Ⅶ, Ⅷ in Ⅲ -grade sequence, which was conducive to forming a large thickness of dark mudstone. Sedimentary sequence had a stretching feature. The evolution of sedimentary basins was closely related to tectonic activities, and tectonic activities controlled the sea level change. The history of regional tectonic activities could be further studied through regional stratigraphy and sequence stratigraphy analysis, so that the favorable environment for dark mudstone formation could be predicted.