Abstract: In order to do a better job for prevention and control of coal spontaneous combustion in Baozigou Coal Mine, the article analyzes the experimental data of spontaneous combustion, studies the laws and characteristics of coal spontaneous combustion in Baozigou Coal Mine, analyzes and optimizes the mark gas, and determines the critical oxygen concentration for coal spontaneous combustion. The results show that the critical temperature of CO, C₂H₄ and C₃H₆ gas is at 62 ℃, 165 ℃ and 220 ℃, respectively. CO can be used as the mark gas for predicting coal spontaneous combustion, and the critical oxygen concentration of coal spontaneous combustion is 7.0%.