Abstract: In order to investigate the factors affected to the coal gas desorption, the diffusion, adsorption and other theory combined were applied to derive a gas d esorption equation.The equation showed that the adsorption balance pressure, particle size of the coal sample, coal failure type and desorption time were the major fac tors affected to the gas desorption of particle coal.In order to verify the reliability of theoretical derivation, those four factors affected to gas desorption of the particle co al were investigated individually in the lab.The results showed that the smaller particle size of the coal sample, the higher adsorption balance pressure would be, the se rious failure of the coal sample would be and the higher gas desorption value within the same time would be. The relationship curve between the gas desorption value a nd time of any coal sample under any conditions would be a monotone increasing function and the longer of the time, the higher total desorption value would be.The tes t results and theoretical derivation would have a consistency.