Abstract: A great breakthrough was achieved in Cretaceous Qingshuihe formation of Sikeshu sag in the southern margin of Junggar basin in January, 2019, and more than one thousand tons of commercial oil and gas flow per day has been obtained from the Well Gaotan-1, which set a new record of well daily production in Junggar basin. Meanwhile, the great exploration potential in Sikeshu sag of Junggar basin has been proved. To accurately evaluate the resources in Sikeshu sag and provide a basis for exploration deployment, the paper systematically analyzes the hydrocarbon properties in the well and its surrounding exploration wells and the characteristics of Jurassic source rocks, and discusses the relationship between hydrocarbon generation and accumulation in the sag. The study shows that the gas-oil ratio（GOR）of the Cretaceous pay zone in the Well Gaotan-1 is 260~360 m3/m3, and the crude oil is light oil with low density and low viscosity. The carbon isotope ratio of the crude oil is -26.83‰ with Pr/Ph as high as 3.6, and the abundance of tricyclic terpane C19, C20 and C21 decrease gradually, indicating typical geochemical characteristics of coal-bearing source rocks. The natural gas in the Well Gaotan-1 is exinite-rich, humic-type wet gas with the methane content of 74.44%, the carbon isotope ratio of methane and ethane of -40.35‰ and -28.74‰, respectively. The above hydrocarbon characteristics indicate that the oil and gas in the Well Gaotan-1 mainly come from Jurassic source rocks with the organic phase of D/E. The systematic source rock analysis shows that the source rocks of D/E and F organic phases are developed in the Middle—Lower Jurassic strata in Sikeshu sag, and the sag center is in condensate oil—wet gas stage and has high hydrocarbon generating potential. It is considered that the Jurassic petroleum system in the study area has great exploration potential