Abstract: Combined with theory analysis, experimental study and numerical simulation, the dynamic adsorption and desorption experiment of coal on gas were carried on for coal samples from same coal quality but different particle size under constant temperature conditions with the help of coal gas adsorption and desorption experiment system. At the same time, the mathematical model of one-dimensional unsteady gas flow was built, which was disposed with finite difference method. The computer software was designed with visual basic to solve the mathematical model. Through the contrastive analysis of theoretical calculation results and experiment results, the conclusions show that the gas flow in the coal partical corresponds to Darcy law.