Based on core, logging and logging data, the high⁃precision sequence stratigraphic framework in Nantun formation of Wunan subsag, Wuerxun depression, Hailar basin and the distribution characteristics of sedimentary systems under its control are studied. The results show that there are five types of sequence boundaries in Nantun formation, which can be divided into three third⁃order sequences and nine fourth⁃order sequences. Throughout the variation of residual stratum thickness of each sequence, it can be found that the sedimentation center of Nantun formation moved westward gradually, and the stratum distribution characteristics changed from "moderate thickness to east and west thin" to "west thick to east thin" gradually from bottom to top. During the sedimentary period of Nantun formation in Wunan subsag, four sedimentary systems were developed, including braided river delta, fan delta, sublacustrine fan and lake. Each sedimentary system has the characteristics of "east⁃west zoning". The fan delta sedimentary system mainly develops in the western Wuxi steep slope zone, and the braided river delta sedimentary system mainly develops in the eastern Wudong gentle slope zone. The distribution characteristics of sedimentary system in different periods have obvious inheritance.