Abstract: Based on the analyses of natural gases from three gas fields and three oil fields,the composition and plane distribution of natural gases in the Lishu Fault Depression of the Songliao Basin were discussed and the genetic types of gas were identified.Natural gas in the Lishu Fault Depression contains significant alkane gases and a little nonhydrocarbon gases,especially CO₂.Alkane gases and CO₂ were organic genesis and there were three genetic types of alkane gases in the Lishu Fault Depression.The first type was mixed by oil-type gases with different maturities,mainly located in Pijia gas field,Bawu and Siwujia oil fields,with partly reserved order of δ13C.The second type was coal gases with high and over maturity,located in Gujiazi gas field and Xinli oil field,with reversed order of δ13C.The third type was mixed by oil-type gas and coal gas,located in Houwujiahu gas field.