Abstract: Based on drilling data of Chunxiao No.1 well in Chunxiao area, Southern Xihu Trough, and interpreted with sequence stratigraphic analysis of seismic profile, this paper establishes terrigenous basin-fill succession, varieties of sedimentary system and evolution periods of depositional process in Oligocene basin-fills, and briefly discusses various genesis of coarse clastic deposits in the lower part of Huagang Formation.