Abstract: The effect of adsorption time, particle size and moisture on initial speed of methane diffusion is measured through test, which is analyzed by fick's laws. All these provide the theoretical basis for revealing the mechanism of coal adsorption desorption gas. Results show that the effort of adsorption time on initial speed of methane diffusion is very great before absorbing saturation; the absorption time couldn't affect the initial speed of methane diffusion after absorbing saturation; with particle size decreasing the initial speed of methane diffusion increases; with moisture increasing the initial speed of methane diffusion reduces increases.