Abstract: The Yanqi basin is located in the east of South Tianshan orogenic belt. As a small Jurassic petroleum basin,the Yanqi basin,which is similar to the surrounding basins such as the Tarim,and the Tupan basins,has its owns peculiar characteristics of petroleum geology. This study,based on the essential characteristics of generation,reservoir,cap rocks,and trap,focuses on the conditions of the petroleum formation of Bohu depression. Through organic matter types,abundance and degree of thermal evolution,it shows that pelites of the lower Jurassic Badaowan group are main hydrocarbon source rocks. The reservoir has low porosity and permeability and drilling data indicate there are two suites of reservoir-cover. Hydrocarbon generation history,authigenici llite chronological study and homogenization temperatures of fluid inclusions,show that there have two stages of petroleum generation and accumulation.