Abstract: Abstract：The Yanqi basin of Xinjiang is a Meso-Cenozoic basin. According to the field survey and strata/rock geochemical analysis of the Lower Jurassic Badaowan Formation in the basin, the authors think that: the source area lies in the north of the basin and fragments were transported from north to south, with coarse fragments deposited in the north and fine fragments in the south; braided stream facies sediments occur in the north of the Yanqi basin, while lakeshore and shallow lake facies sediments in the south; and the new apatite fission track data show that the mountains on the western, southern, and northern margins of the Yanqi basin were uplifted late; and Jurassic strata still remain in mountains around the Yanqi basin at present. All these show that the primary sedimentary boundary of the basin is wider than that of the present basin. Based on the above analysis and its comparison with the Kuqa basin, the authors find that the Yanqi basin was connected with the Kuqa basin and that the two basins were a part of the Tarim basin in the Badaowanian period.