Abstract: To study gas desorption diffusion law of coal particle has important realistic meanings to gas content determination of coal seam by use of desorption method and outburst risk prediction of coal seam. Because of various factors including geological conditions, the physical and mechanical properties of coal seam, the drilling process, the coal sample will present different shapes, whose parameters about gas desorption diffusion will be not the same. The mathematical simulation was done for the effect of different shapes on gas desorption diffusion law, which the coal particle shape could be distinguished by our naked eyes from a macroscopic view. And the mathematical models of gas desorption diffusion and its analytical solutions were obtained under different coal particle shapes. And considering the different desorption diffusion time, the approximation formulas of the different gas desorption diffusion models were obtained. Through the comparison and analysis, in distribution range of the same particle size , the preliminary stage of coal gas desorption is more heavily influenced by the shape; but with the extension of the desorption time, it has smaller role on gas desorption diffusion. The effective shapes of gas diffusion under the different shapes of coal particles have gradually approximated to sphere.