Abstract: The oil and gas potential of Baoshi Formation in the K gas field of Xihu Sag is considerable, but its paleogeographic environment is not clear. In this paper, on the basis of the "source-ditch-sink" comprehensive analysis, the sedimentary system evolution and distribution of Baoshi Formation in the K gas field are studied by means of seismic and drilling data, and the sedimentary facies types and distribution rules of Baoshi Formation are defined. The results show that Baoshi Formation can be divided into the upper and the lower members and its sediments mainly come from the reef bulge in the northwest. Baoshi Formation of the K gas field mainly develops delta front subfacies deposits, including sand bar, distributary main channel, distributary secondary channel and interchannel sedimentary microfacies. The south and the north subdepressions in the research area are the dominant sedimentary convergence regions. The underwater distributary channel of the upper member and sand bar of the lower are favorable targets for further exploration and development. This study can provide reference for the petroleum exploration of Baoshi Formation in the K gas field.