Abstract: Under proper outside conditions, the absorped gas in the coal will quickly desorb into free gas, release enormous energy and thus produce a strong gas dynamic effect. Through the theoretical analysis, the key factors affecting the gas desorption velocity-the gas concentration gradient and the pore wall energy barrier were obtained. Under certain conditions of coal seams, the concentration gradient of the absorbed gas depended on the release velocity of the high-pressure gas in the external fracture, and there was a close relation between the energy barrier of pore wall and the particle sizes of coal. In this paper, analysis was carried out on the influence of different adsorption pressures and particle sizes of coal smaples upon the gas desorption features, and the the change rule of the gas desorption velocity and quantity with the pore pressure and the damage degree of coal was obtained.