Abstract: Based on the analysis of related data in coalfield outcrop fire area, MTLT-100 type coalfield outcrop fire similar simulation experiment device was designed independently, and the similar simulation experiment was carried out. Through the determination analysis of the gases including O_2, CO, C₂H₆, C₃H₈, C₂H₄ and C₂H₂, the followed results show that: when coalfield outcrop fire coefficient R₂ increased to 0.5, coalfield outcrop fire is developed from low temperature oxidation preheating process to the high temperature accelerated oxidation preheating process; when R₂ increased to 0.8, fire is developed from high temperature accelerated oxidation preheating process to stable smoldering process; when the R₂ is in a state of decline, fire is in the process of smoldering suffocation. When fire is in the process of stable smoldering, the fire area temperature is generally about 300 ℃, and it is below 300 ℃ in the rest of process.