To reveal the genetic mechanism of Jurassic heavy crude oil in the northwest margin of Jugar Basin, the physical property, group composition and distribution rule of heavy crude oil are analyzed, and researches on hydrocarbon migrating and accumulating in the Jurassic period of this area are associated with, the heavy oil evolution is recovered. The studies manifest that primary oil gas pool in Permian Formation has been superposed and deformed by tectonic movements, thus the hydrocarbon has occurred second migration and accumulated into the overlap Jurassic Formation. In the process of the migration and accumulation, the hydrocarbon has become thicker in according with oxidation and biodegradation, and in the later stage through the virtue of tectonic movement and watered affection, the distribution of heavier crude oil has formed. Heavy oil is favorable for the formation of reservoir and the formation is a quite complicated procedure involving complex geological and geochemical function, therefore, the research on its genetic mechanism plays an important role in the exploration and exploitation.