Abstract: Hutubi and Huoerguosi oil and gas field is located in the southern margin of the Zhungeer basin in China,it is rich in oil and gas resources,it is the important oil and gas field in our country western,the natural gas identification in terms of origin,especially in kerogen and oil cracking gas identification is still controversial,aiming at this problem,in a large number of basic data statistics and experimental analysis,we have choose the parameter of Ln(C₁/C₂),Ln(C₂/C₃),C₁/C₃ and C₂/C₃,C₂/iC₄ and C₂/C₃,δ¹³C₃ and C₂/C₃,δ¹³C₁ and δ¹³C₂ as the index,to identified the natural gas in Hutubi and Huoerguosi oil and gas field,and think that they are kerogen cracking gas and mainly from the Jurassic.The simulation of crude oil cracked gas dynamics and the simulation isotope dynamics showed that the crude oil cracking gas conversion rate is very low,so that the gas in that two oil and gas fields are mainly from kerogen cracking.