Abstract: The filtration and purification effect of the seam roof fracture zone on improving the concentration of gas drainage is generally recognized. Gas drainage technology of high-level borehole in fracture zone has also been widely used in gas prevention and control of mining face.In order to study the mechanism of gas filtration and purification, the spatial network structure formed in the fracture zone of coal seam roof is studied by combining theoretical analysis with CT scanning verification experiment. The results show that: there are a large number of macroscopic and microscopic fractures caused by mining in the caving zone, fracture zone and bending subsidence zone above the goaf of the mining face; the geometric size of the fractures gradually decreases, presenting a huge spatial reticular structure; the macroscopic fractures in the caving zone and the lower part of the fracture zone have a higher concentration of gas near the upper part due to the strong diffusion of CH₄, and the microscopic fracture net in the middle and upper part of the fracture zone is similar to a huge thick filter membrane,which further inproves the CH₄ concentration through viscous flow and Knudsen diffusion filtration.The engineering test results of dangjiahe coal mine in Fuxian show that the upper of the fracture zone with a vertical height of 16-18 m above the roof of the coal seam is the best filtration space of CH₄, and the gas drainage concentration is generally above 50%, up to 73%. It is verified that the spatial reticular structure of the coal seam roof fracture zone is correct to filter and purify CH₄. The research results have certain guiding significance for the arrangement of high-level drainage boreholes and the efficient drainage and utilization of mine gas.