The Xiaohaizi section in Bachu area of Tarim basin is one of the most complete and best exposed areas of Carboniferous in the basin, and the study of this section will help to understand this stratum. According to field observation and analysis, it is considered that the Upper Devonian - Carboniferous of the Xiaohaizi section is mainly a set of shallow sea facies sedimentary bodies. The lower part is mainly developed with wave-controlled clastic shore deposits; the middle part is dominated by open platform, lagoon and restricted platform environment; the upper part is mainly composed of thick-bedded of evaporation platform gypsum; the top part shows the restricted platform characteristics of mixed carbonate and siliciclastic sediments. Combined with the stratigraphic distribution and tectonic evolution of the basin, it is considered that the Upper Devonian - Carboniferous sediments in the Xiaohaizi section can be divided into four stages from bottom to top: clastic rock, mixed deposit, gypsum rock and mixed deposit.