Abstract: In order to investigate the influence of coal moisture on the solidity coefficient f of coal and initial speed of methane diffusion△p, the moisture content of each coal sample in different experiments was made and each coal sample soaked in water for different time, and then measured coal samples f and △p; experimental study found that coal moisture content increased with the coal sample immersion time prolonged, coal firmness coefficient increased, and the initial speed of methane diffusion decreased, and coal moisture had greater impact on these two indexes. Therefore, it is necessary to limit the moisture in the outburst parameters determination process of coal samples.