The authors comparatively studied the geochemical characteristics of C6-C7 light hydrocarbons in natural gas from Lishu fault depression in Songliao basin for the first time. Combined with characteristics of carbon isotope, results showed that natural gas from Lishu fault depression is very poor in aromatic hydrocarbon but rich in chain alkanes. The distribution characteristics suggested that the natural gas originated from sapropelic organic matter. The ratio K1 is around 1 and the three-ring preference (3RP) is greater than 5RP and 6RP in C7 light hydrocarbon from lacustrine facies source rocks, which were basically consistent with the conclusion of light hydrocarbons by Mango. The high value of paraffin index and heptane index indicated that the natural gas is mainly pyrolysis gas which coincides with the high value of δ13C1.