Abstract: Well Shinan 31 locates in the north of the Shixi Oilfield,the hindland of Junggar Basin.It's another major discovery after finding the Jurassic Toutunhe Formation reservoir in the Well Shinan 21.The reservoir is in the Cretaceous Qingshuihe Formation with high gas and oil ratio and light oil,while associating with the black biological degradation oil.The article applies entire hydrocarbon geochemical methods to confirm the origin of the oil-gas.It pointed out that the oil and gas was from the Wuerhe Formation source rock in the western Well Pen 1 Sag.It also clarified the oil and gas genetic relationship between Cretaceous oil and gas in Well Shinan 31 and Carboniferous and Jurassic oil and gas in Shixi Oilfield.It established the hydrocarbon formation mode of the Cretaceous reservoir in Well Shinan 31 and pointed out that the chief exploration target in the near future is the oil and gas captured by the transition region between the Shixi Oilfield and Well Shinan 31 during its migrating from south to north.