Abstract: In order to study the composition characteristics of fracture network and the law of gas flow after coal and rock are loaded, this paper uses CT scanning technology to study the changes of fracture microscopic parameters and macroscopic fracture morphological characteristics during the loading process of coal and rock, and COMSOL numerical simulation is used to study the interaction law between coal and rock fracture and gas fluid in the process of gas flow. The results show that the fissure aperture degree of sandstone, alluvial clay and coal specimens is concentrated in 0.1-0.2mm after loading failure, and the crack dip angle is concentrated in 80°-90°, 55°-70° and 50°-90° respectively. The different length and expansion direction of the fracture lead to different fracture morphology. The sandstone penetrates the upper and lower surfaces of the rock, and the overall damage is serious. After the failure, it is ' double inclined plane shear failure ', and the coal specimen is ' single inclined plane shear failure '. The permeability of sandstone fractures is large, and the flow velocity on the whole section exceeds 0.01 m/s. The flow velocity growth area of clay and coal specimens is small. Affected by the gas flow pressure, the area where the internal pressure of the sandstone specimen is greater than 0.5 MPa is the largest, with a volume ratio of 21%, an alluvial clay volume ratio of 16%, and a coal specimen volume ratio of 11%. The change of fracture morphology causes the change of gas pressure gradient. The shape of gas pressure distribution in the vertical fracture area increases linearly, and the shape of gas pressure distribution in the fracture tip area changes with a quadratic function.