Abstract: The Xihu Sag with relatively great exploration breakthrough in the East China Sea shelf basin has a great exploration potential.Huagang Formation of the Xihu Sag holds good petroleum geology conditions,which has multiple hydrocarbon sources in which the main is Pinghu Formation,and good reservoirs and regional seals are well developed.Structural trap is the main trap type,such as rollover anticline and compression anticline trap,and oil-gas reservoirs are also belong to these two types.Based on the analysis of the petroleum geology and hydrocarbon distribution pattern of the Huagang Formation,it is considered that the western part mainly contains oil,while the eastern part mainly contoins gas,and the main hydrocarbon distributes in the middle and southern part of the Xihu Sag in which the structure is more locally developed.