Based on the capillary hypothesis and fractal theory, a mathematical model for calculating the effective gas diffusion coefficient in porous media was established. By using the fractal geometry theory, the pore area fractal dimension, the tortuosity fractal dimension and the pore connectivity were introduced to quantitatively characterize the real internal structure in the porous media, and the fractal model for the microscopic pore structure in the porous media was established. The gas diffusion in the porous media on different scales was systematically studied. An effective gas diffusion coefficient model for the fractal porous media was derived, and the influence of multi-scale porous media microstructure parameters on the effective gas diffusion coefficient was discussed. The results show that effective gas diffusion coefficient approximates to linearly increase with the increase of porosity, the pore area fractal dimension and the effective gas diffusion coefficient is positive correlation, but the tortuosity fractal dimension is negative correlation with it. In the case of different porosities, the gas effective diffusion coefficient varies with the change of the pore diameter ratio, the effective gas diffusion coefficient increases with the increase of pore connectivity. © 2019, Editorial Department of Journal of Southeast University. All right reserved.