Abstract: In theudy of fracture structure, the image processing with conventional X-ray or CT scanning will be accompanied by a large number of secondary fractures, and the main fracture characteristics are not obvious, which can not directly reflect the relationship between fracture structure and fluid velocity. High definition camera is used to take X-shaped real cracks in coal wall for digital processing, and the characteristics of fractures are extracted by CAD software, and the images are vectorized into the model, the distribution nephogram of seepage velocity field and seepage pressure field is obtained by simulating software. The results show that from the entrance, the seepage pressure decreases from the left to the right, are evenly distributed in the fracture channels, the fracture area fully releases the pressure, which is a pressure buffer zone; the distribution of seepage velocity field in the rock mass is uneven, the seepage in the tributary area is more active than that in the confluence area, and the angle between the gas flow direction and the fracture direction has obvious influence on the seepage velocity. The maximum seepage velocity of gas in the same flow direction is 29.5 times. There is a logarithmic function relationship between the seepage velocity in the fracture channel and the fracture size. When the fracture size is 0.68-1.23 mm, the seepage velocity is most obvious. The research results could be used to understand the characteristic of gas seepage flow in coal fractures intuitively.