According to the geochemical characteristics of crude oil, reservoir bitumen and source rocks, the origin of viscous oil and reservoir bitumen was analyzed. The effects of bitumen and viscous oil on the exploration were researched. The results show that the viscous oil distributes widely in Jurassic and Triassic formations, and the reservoir bitumen distributes mainly in the Toutunhe formation and above the formation. The heavy viscous oil and reservior bitumen all derived from the result that the low-maturity crude oil suffered from loss and strong biodegradation. The medium density oil comes from the result that the mature oil suffered from loss and moderate biodegradation.