Abstract: In order to improve the assessment accuracy of gas drainage volume from the residual coal in coal mine gob, a self-developed simulation testing device for gas desorption from residual coal in the gob was used to simulate the gas desorption process from coal samples with different particle sizes under the condition of a simulated air-sealed gob, the functional relation expression of the gas desorption velocity from residual coal with the time and particle size and the empirical calculating formula for the cumulative gas desorption volume of the residual coal were fitted and derived. It was verified that the derived formula for the gas desorption from residual coal could better describe the influence of the particle size on the gas desorption rule of the coal sample and also better reflect the influence of the particle size on the cumulative gas desorption volume.