Abstract: In this paper, based on the adsorption tests of coal particles with different sizes, dual combined first-order rate function model is established to calculate and analyze the gas adsorption process of coal particle. The results show that the gas adsorption process in coal is a combination of macro migration and micro continuous adsorption in the pores, and the perfect fitting for test data can be achieved by using the dual first-order function combination model. With the increase of particle size, the half-life time of methane adsorption(fast and slow adsorption process)increases. The smaller the particle size is, the larger the adsorption capacity is under the same adsorption equilibrium pressure.