Abstract: Through analyzing the hydrocarbon shows statistics, gas components of drilling mud and methane carbon isotope of different Formations, including Cretaceous Ejina Banner Formation, Jurassic Mamuwusu Formation and Paleozoic superface weathered crust of X well in Ejina Banner region, we suggest that Jurassic and Cretaceous have the same hydrocarbon shows statistics, namely oil and gas shows, and the dry coefficient of gas samples ranging 0.80~0.87, the average methane carbon isotope (δ13C1) ranging -48.19‰~-50.87‰, which show that the gas has and the characteristics of low mature pyrolysis gas. Palaeozoic weathering crust is gas shows, with the dry coefficient ranging 0.91~0.92, and the average methane carbon isotope (δ13C1) is -21.56‰, indicating that the gas has the characteristics of high mature pyrolysis gas. The kerogen types and evolution degree are remarkable different between Mesozoic and Palaeozoic sources rocks of X well and its vicinity. Mesozoic sources rocks are low mature mixed kerogen, and Palaeozoic sources rocks are mature- high mature (over mature) mixed-sapropelic kerogen. It shows that there are petroleum system of Mesozic Jurassic-Cretaceous low mature source rocks as hydrocarbon source and Palaeozoic high mature source rocks as hydrocarbon source, which indicate the hydrocarbon prospects of Palaeozoic.