Abstract: In order to study the influence of water on coal adsorption /desorption of CH₄, a dynamic test device for coal seam gas adsorption and desorption deformation was used to carry out the CH₄ adsorption/desorption tests of lump coal with moisture content of 0, 0.83%, 1.52% and 2.68%. The results show that water has a significant effect on the adsorption/desorption of CH₄ by coal. Water helps the desorption of CH₄ by coal, but inhibits the adsorption of CH₄ by coal. The value of the saturation adsorption a and saturation desorption A are basically equal, and has no relationship with moisture content. The value of adsorption constant b and desorption constant B shows an exponential decreasing trend with the increase of moisture content in coal, and finally approaches 0. Based on the Langmuir equation form and functional relationship between the adsorption/desorption constants and moisture content, the CH₄ adsorption/desorption mathematical models under the influence of moisture content were constructed, and were verified using experimental data. The difference coefficient of adsorption and desorption showed an exponential decay trend with the increase of moisture content.