Abstract: The Yanqi and Qaidam Basins are two Jurassic ones in the northwest China. The difference between the both in the strength of tectonism during the Meso-Cenozoic resulted in some differences in ages of petroleum generation and accumulation, and in occurrences of the petroleum. According to the results of the simulation of petroleum generation, the data of homogenization temperatures and the normal hydrocarbons of the inclusions in the Jurassic reservoirs, it was concluded that the petroleum in the Yanqi Basin mainly generated at the end of the Middle Jurassic, and the petroleum accumulated during Late Jurassic and Early Cretaceous; there were two generations of the petroleum in north region of the Qaidam Basin, generated in Middle Jurassic and Early Neogene respectively, and accumulated mainly in Neogene. Both of the basins represented two accumulational models in NW China: early accumulation in Jurassic reservoirs and late accumulation in Tertiary reservoirs, respectively.