Abstract: In order to clarify the effect of small volume on the spontaneous combustion of coal, in this paper, the laws of gas generation under different airflow （1, 2 mL/ min and 3 mL / min） were studied. The results show that the coal sample can still be oxidized when the oxygen concentration is 13.08% at room temperature. The smaller the airflow, the lower the oxygen concentration, the higher the concentration of CO gas is. When the amount of air supply in the working face is reduced, the concentration of CO gas in the gob is high, and the longer the time is, the greater the concentration of CO gas in the gob, however, there is no proof that the temperature of goaf is rising.