Abstract: The degree of coal pulverization leads to the difference of gas adsorption state in coal, which has an important impact on the gas migration time in coal pores. The research results play an important role in improving the accuracy of gas content determination in coal. In this paper, coal samples from Machang Mine were chosen as the research object to observe the relationship between particle size and the equilibrium time, the adsorption isotherms and the adsorption equilibrium time of coal with four degrees of particle sizes are measured in the laboratory. The conclusions are as follows: the smaller the degree of particle sizes is, the larger the gas adsorption capacity of coal sample is. The isotherms can be divided into four parts: “micron, ten microns and small particle size hundred microns, large particle size hundred microns and millimeter”. With the increase of particle size degree, coal sample adsorption equilibrium time is rapidly increasing, in which, the adsorption equilibrium time for the coal sample with the minimum particle size was only 5 min, but for the largest particle size was more than dozens of days, which means that the impact of diffusion path will increase rapidly with the increase of degree of particle sizes. Comprehensive analysis shows that the adsorption equilibrium time of coal sample with 100 μm particle size can be significantly shortened and the gas content determination accuracy can be improved.