Abstract: An intensive analysis of the characteristics of main gas fields in central and northwest Sichuan basin such as the components and migration indicators of natural gas shows that natural gas of Xujiahe Formation in central Sichuan basin was mainly generated from source beds in the hydrocarbon generation sags,and the natural gas of T3x2, T3x4, T3x6 was respectively generated from hydrocarbon source rocks of T3x1, T3x3, T3x5. It is pointed out that even if the gas generation intensity of hydrocarbon source rocks in the hydrocarbon generation sag is lower than 20×108m3/km2,the reservoir which has good physical properties and beneficial tectonic background and is close to the hydrocarbon generation sag could also form a large or medium sized gas field.