Fan delta, which is developed on the steep slope belt on the south side of the sag, is an important sedimentary facies of Dainan Formation in Gaoyou Sag of Subei Basin. According to single well and cross well sedimentary facies analysis, seismic profile reflection and sand ratio contour map analysis, planar distributions of sedimentary facies in different submembers of Dainan Formation were confirmed, and the distribution maps of sedimentary facies in different submembers were drawn. The results showed that the steep slope paleogeography in the southern part of Gaoyou Sag was a suitable condition, and sedimentary structures reflecting traction flow and gravity flow were found.