Abstract: The Changde gas reservoir in the Songliao Basin is the only inorganic gas reservoir in the world which mainly produces alkane gas with a full geochemical complement. Therefore, the study of Changde inorganic gas reservoir has a great significance for the development of China's natural gas exploration. We designed a geochemical profile crossing wells Fangshen1 and Fangshen2 above the Changde gas reservoir, studied the near-surface display of different geochemical indicators, and selected effective geochemical methods and abnormal indicators. The analysis of methane carbon isotopes can help judge the inorganic origin of the reservoir.