Abstract: The characteristics of coal spontaneous combustion were investigated through programmed temperature experiment and the concentration of CO, CO₂ etc for coal with various sizes was measured at different temperatures. The selection of index gases was discussed. The law of concentration change for CO, CO₂ etc and the relation of consuming oxygen velocity to coal temperature and size were analyzed. The smaller the coal size and the higher the temperature, the more intense the reaction of coal and oxygen. The results can direct the prevention and treatment of fire in mine.