Abstract: Based on the analyses of various isotopic compositions (δ¹³C₁,δ¹³C_co2,⁴⁰Ar/³⁸Ar,etc.),it is suggested there arc not only natural gases of single origin,but also gases of mixed origins.According to the isotopic composition studies of He,Ar and C,the constituents of He,Ar and N₂ in Sinian weiyun Gas Field are pertained to inorganic origin coming from deep parts of the crust,whereas it can attributed to thermogenic gas because the isotopic values of the hydrocarbons are of -32.6‰— -32.9‰.As another example,the gas of Wanjints Gas Field has values of δ¹³C_co2 range from -4.04‰ to -8.83‰ which proves the inorganic origin of the CO₂ (volcanic source) whereas δ¹³C₁ value is of -42.07‰ to -45.37‰ which indicates the organic origin of the methane.The various origins of the different constituents of the same gas pool (shows) indicate not only the complex processes for the accumulation and formation of natural gas,but also the complication of the gas and source correlations.