The Pinghu Formation and Huagang Formation in the Xihu Depression are the main targets for ail exploration in this region, They could be divided into five third-order sequences of SⅢ1, SⅢ2, SⅢ3, SⅢ4, SⅢ5, according to subsurface geology, geophysics and laboratory testing data. For the sequences of SⅢ1 and SⅢ2, the authors proposed three stratigraphic models, i.e. fault terrace, subwater uplift and half graben models. A infilling model was constructed for the sequence SⅢ3, and a downwarp model for the sequences of SⅢ4 and SⅢ5. Sedimentary evolutionary history within the sequence framework was reconstructed, and its implication for petroleum geology was discussed.