Abstract: In order to further investigate the characteristics and laws of gas desorption and diffusion in coal seam, the study designs the experiment system of gas adsorption and desorption in coal sample. The system mainly consists of several subsystems including a temperature control system, an adsorption and desorption experiment system, and a data collection and disposing system. The experiment studies the isothermal desorption and diffusion laws of two kinds of coal, two kinds of granularity of four different coal samples under constant temperature at 30 ℃ and different adsorption equilibrium pressures. By comparing and analyzing the data of four types of coal samples, the relationship between gas desorption quantity and time is obtained. The study establishes cumulative desorption mathematical model of coal gas and analyzes the factors of parameters on model change.