Abstract: In this paper, the real fracture structure of coal is obtained by SEM technology to solve the problem of non-uniformity characterization of coal. Based on the characteristics of fracture structure, the dynamic characteristics of gas flow are calculated by solving the Stokes equation by COMSOL. The calculation model of gas permeability is established, and the influence of fracture opening on permeability is studied quantitatively. The results show that the fracture opening has great influence on the permeability of CBM. When the Klinkenberg effect is considered, the gas crack flow model is modified.