Abstract: In order to study influence of adsorption pressure and grain size of coal sample on coal gas desorption, the No.3 coal in Sihe Coal Mine was selected as samples, and variety characteristics of gas desorption amount and desorption speed of coal samples with 0.17-0.25, 0.25-0.50, 1-3 mm grain sizes were analyzed at 1, 1.5, 3 MPa adsorption pressure by use of a gas isothermal adsorption and desorption experiment system. The experimental results show that under different adsorption pressure conditions, the gas desorption amount of the coal samples and initial desorption speed increase with the increase of adsorption on the whole. However, the influence of adsorption pressure on gas desorption amount and desorption speed of coal samples with 0.25-0.50 mm grain size is smaller than the other two grain sizes. The initial gas desorption amount of coal samples with smaller grain sizes is more than the one of the coal sample with bigger grain size under different adsorption pressure conditions, and the initial desorption speed is faster. But the gas desorption amount of the coal sample with 1.0-3.0 mm grain size is more than the one of the others under 1.5, 3 MPa adsorption pressure condition. Therefore, increasing adsorption pressure of coal sample or reducing grain size would cause increase of gas desorption amount and desorption speed.