Abstract: Guided by sequence stratigraphy and based on seismic, drilling and well logging data in Hulihai sag of Qianjiadian Depression, analyzing the background of structural evolution and sedimentary environment, climate condition, Cretaceous sequence can be subdivided into one first-order sequence, two second-order sequence, six third-order sequence. SⅢ1 (Lower Cretaceous Jiufotang Formation) develops completely, which is composed of lowstand, transgressive and highstand system tracts. According to the characteristics of sequence development and based on division and comparison of sequence formation units, sedimentary types and system are studied. It is concluded that S Ⅲ 1 in Hulihai sag features in near and more provenances, rapid subsidence and rapid deposition. The highstand system of SⅢ1 develops nearshore subaqueous fans in the west steep slope belt, and fan delta in the east gentle belt. Shore-shallow lacustrine and deep lacustrine facies are recognized in the central sag; turbidite fan is distributed in some area. The sequence, which is between the transgressive system tract of the second and the third-order sequence, has the best source rocks and sealing conditions as well as various favorable reservoirs. So it is the most favorable target for obtaining discoveries in Hulihai sag.