Abstract: The coal can release a series of gas in the process of oxidation and spontaneous combustion,and different stages correspond to different gas composition and concentration.Therefore,analyzing the composition and the concentration of the gas,the occurrence and development degree of coal spontaneous combustion underground coal mine can be predicted.Thus,selecting the indicator gas accurately plays a very important role in preventing the coal spontaneous combustion.Combined with field sampling,this paper selected the suitable indicator gases for No.3_up coal seam in Qiwu coal mine by the pyrolysis experiment.