Abstract: By analyzing the acidolysis hydrocarbon in 33 sandstone samples from Sifangtai Formation in the western slope of Songliao Basin, the paper discusses the composition, genesis and origin of hydrocarbon gas, and preliminarily analyzes the relation between hydrocarbon fluids and sandstone-type uranium metallogenesis combined with the geological characteristics of uranium mineralization in the area. The characteristic parameters of C₁/ΣC, C₁/C₂₊, C₂/iC₄, C₂/C₃, iC₄/nC₄ and iC₅/nC₅ for gas compositions in acidolysis hydrocarbon show that the hydrocarbon gas in the bottom sandstone of Sifangtai Formation is of organic origin, mainly in the maturity-high maturity stage, which are crude oil cracking gas and associated mixture gas, migrating to the bottom sandstone along superficial faults. The content of hydrocarbon fluids in uranium-bearing sandstone of Sifangtai Formation is generally increased, indicating the uranium mineralization is closely related to hydrocarbon gases. The place near the superficial fault connecting the bottom of Sifangtai Formation and oil-gas field is the key area for sandstone-type uranium deposit prospecting in the western slope.