Abstract: To find out characteristics and controlling factors of beach?bar sand bodies in a terrestrial down?warped lacustrine basin is of great significance for lithologic reservoir exploration in it. In this paper, the characteristics of beach bars of transgressive systems tract and highstand systems tract of Huangshanjie formation of the Upper Triassic in Tabei area (northern Tarim basin) were analyzed in detail, based on the drilling, well log and3D seismic data. The results show that five microfacies are identified in the beach bars, including bar body, bar edge, interbar, beach sand and lake bay, with each microfacies having different sedimentary characteristics. The beach bars mainly develop in the northwestern and northeastern Tabei, dominated by northwestern Tabei on the plane, and in other areas they are isolated distribution. The formation of beach bars is closely related to the special paleogeomorphology setting, hydrodynamic environment, lake level change and provenance supply. Finally, based on the analysis of sedimentary characteristics, distribution and controlling factors of the beach bars, the depositional model for such beach bars in the down?warped lacustrine basin is established