Abstract: Taking the desorbed gas in the shale cores of the Chang 7 Oil Member in Well WX of Fuxian area, Ordos basin as the study object, the geochemical characteristics such as gas component, light hydrocarbon, carbon isotope and hydrogen isotope in the shale cores are studied, based on which the genesis of the natural gas are analyzed. The results show that the characteristics of gas component, light hydrocarbon composition, carbon isotope and hydrogen isotope of the shale gas are significantly different among samples obtained from different depths of the Chang 7 Oil Member in Well WX. With the increase of the depth, heavy hydrocarbon contents, relative contents of n-alkanes and isoalkanes in light hydrocarbons and the ratios of n-alkanes and isoalkanes contents to 1,1-dimethylcyclopentanes rise gradually, drying coefficient, naphthene hydrocarbon content and the ratio of naphthene hydrocarbon content to 1,1-dimethylcyclopentanes decrease gradually, carbon and hydrogen isotopes become lighter and the reverse degree of carbon isotope reduces. The shale gas in Chang 7 Oil Member of Well WX belongs to oil-type pyrolysis gases without the mixing with inorganic diagenetic gas and Paleozoic coal-type gas, suffering from different degrees of microbiological oxidization which becomes weaker from shallow to deep. The inhomogeneous microbiological oxidization is the main reason causing the vertical differences of gas component, light hydrocarbon composition, carbon and hydrogen isotopes and carbon isotope reversal in the shale gas of Well WX.