Abstract: 3D seismic data interpretation is systematically carried out by this paper in order to learn the distribution pattern, forming time and genetic mechanisms of the structural traps in the Xihu Sag, East China Sea Basin. Combined with hydrocarbon accumulation conditions, both the main reservoir types and the characteristics of structural traps are revealed. The results show that fault traps and anticline traps dominate the Xihu Sag, among which fault traps are mainly distributed in the slope zone and anticline trap in the inversion zone of the Central Sag. Fault type traps are mainly formed in the rifting stage and controlled by extensional faults and associated structures, while anticline traps mainly formed in the inversion stage controlled by tectonic inversion under a compressional background.The oil and gas reservoirs in the structural traps of the Xihu Sag mainly include the types of faulted nose, faulted block, faulted anticline and anticline. Controlled by source-connected faults, all the oil and gas reservoirs have the characteristics of longitudinal superposition, which resulted in the hydrocarbon accumulations occurred in a pattern with the large in deep, the small in shallow and close to source and fault. In the Late Miocene Longjing movement, the main source faults were reactivated which controlled not only the types of faults and anticlinal traps, but also the accumulation of oil and gas in various structural traps.