Abstract: Coal mine fire caused by spontaneous combustion in coal seam seriously affects the safety of coal mine production. In order to anticipate and prevent the coal seam spontaneous combustion in advance, taking the 3122S working face of Longtan Coal Mine as the research object, combines laboratory coal spontaneous combustion experiments and on-site signature gas testing, and determines the critical value of spontaneous combustion signature gas in coal seam of 3122S working face. Through the temperature programmed oxidation experiment of coal sample, the variation law of gas concentration of coal spontaneous combustion with temperature was obtained, and CO and ethylene C₂H₄ were selected as the main signature gases. According to the fuzzy statistical mathematical method, the critical temperature of spontaneous combustion of coal samples in 3122S working face is calculated to be 87 ℃. By fitting the measured mass concentration and temperature of CO on site and substituting the critical temperature of spontaneous combustion of coal samples, the critical value of the mass concentration of the signature gas CO is calcalated as 88.50 mg/L, and the critical value of the mass concentration of C₂H₄ is 0.90 mg/L. According to the critical value of the signature gas and the temperature monitored on site, the fire caused by spontaneous combustion of coal can be prevented.