Abstract: Oil reservoirs have been found in Triassic Yanchang Formation and Jurassic Zhiluo Formation, Yan’an Formation, Fuxian Formation, and one-billion-tonnage Jiyuan Oilfield has been discovered. Multi-stage lake rise and fall occurred. Distributary channels in deltaic plain, subaqueous distributary channels, mouth bars in delta front and sandy dam of shore lakes, and other types of sand body were well developed during the process. Source rocks are thick with strong hydrocarbon generation and expulsion ability, which generates hydrocarbon pressurization and becomes the main driving force of oil migration along the fracture, fracture-sand, fracture-unconformity, fracture-sand -unconformity, and other conduit system. This kind of migration and accumulation forms multi-layer composite accumulation mechanism. Reservoir tightening and hydrocarbon accumulation is synchronous. Jiyuan Oilfi eld features in hydrocarbon generation pressurization, bilateral expulsion, near-source accumulation, multiple conduit, and differential accumulation. Geological theory innovation, exploration technological advances and constant exploration practice favor the discovery of Jiyuan Oilfi eld.