Abstract: Through SEM indoor experiments of coal-rock, this paper quantitatively describes the parameters of fractures such as length, width, height, density of fractures, establishes quantitative evaluation parameter for fracture permeability, and its influencing factors are studied. The results show that the advantage fracture direction is NE, while the EW direction or NW direction fractures develop in local structural complex area. And the fracture groups are mainly parallel with each other and lie in NW direction, occasional oblique in NW direction. And cross or winding fractures develop in local areas and some fractures are filled with clay mineral and calcite. The length and height of main and secondary fractures of coal rock are similar, and the width and density of secondary fractures are obviously lower than that of main fractures. The fracture permeability index proposed in this paper can effectively characterize the permeability of fractures, and the permeability increases with the increase of the fracture permeability index. When the fracture permeability index is greater than 150, it is a favorable area for CBM development. When the fracture permeability index is less than 100, it is necessary to adopt horizontal well fracturing technology to improve the development effect.