Lower Jurassic Zhenzhuchong Formation and the second number of Upper Triassic Xujiahe Formation are two main gas production strata of Jiulongshan Gas Field, however, no conclusion has yet to be reached about gas source for the both strata. Therefore, this contribution makes a detailed analysis about the gas component, carbon isotopic composition, source rocks and reservoir bitumen biomarkers, to clear the gas sources of Zhenzhuchong Formation and the second number of Xujiahe Formation. It is concluded that gases in the Zhenzhuchong Formation is sourced from the third number of Xujiahe Formation, while gases in the second number of Xujiahe Formation are mainly derived from both the third number of Xujiahe Formation and deep Maokou Formation.