Abstract: The Jurassic natural gas in the western Sichuan depression has the normal series distribution characteristics (δ13C1<δ13C2<δ13C3), which is typical of coal type gas oginated by thermal catalysis. The Kerogen of the natural gas is mainly of the humic type. Through analysis on the rock association characteristics it is suggested that most of the Jurassic natural gas was sourced from the 5th member of Xujiahe Formation of the Upper Triassic. The 4th member of Xujiahe Formation and the Jurassic (such as dark mudstone of the Ziliujing Formation) might also have some contribution for its source. The study on characteristics of light hydrocarbons also indicates important contribution of the 5th member of Xujiahe Formation source rocks. The relationship between δ13C1 and Ro further evidences the same conclusion.