Abstract: A suite of over 100 m thick dolomite was deposited in the Lower Cambrian Xiaoerbulake formation, Tarim basin. Based on the detailed observation and description of the sedimentary and paleontological characteristics of more than 1 000 thin sections obtained from 11 field sections in Keping area, the paper analyzes the petrological and fossil features and sedimentary environment of the Lower Cambrian Xiaoerbulake formation with microfacies analysis method. According to the microscopic characteristics of grain, biogroup and sedimentary fabric of the carbonate rock, 11 microfacies types and 5 microfacies assemblages with similar genesis and certain continuity in vertical variation are identified and classified in the Xiaoerbulake formation. In addition, the results of microfacies analysis also show that the reservoir development of the Xiaoerbulake formation is mainly controlled by sedimentary environment, and the intercrystal (dissolved) pore, intergranular (dissolved) pore and microbial framework pores are the main reservoir spaces. Weak-laminated fine-grained dolomite (MF2) and intraclastic dolomite (MF10) have the best petrophysical properties, and microbial microfacies such as MF6, MF7 and MF8 have relatively good petrophysical properties