Abstract: The traditional fault grouting technology simplifies the fault structure into a single fracture model, which leads to a large difference between the theoretical results and the field construction data. To solve this problem, the grout permeability characteristics under different crack widths, water-cement ratio and grouting pressure were analyzed by using UDEC software. The grouting diffusion rules of single crack model, single crack model and fault orthogonal model are compared, and the field grouting pressure data are used to explain and verify. The results show that the effects of increasing crack width and water-cement ratio on the grout diffusion range are exponential and logarithmic, respectively. There are three types of grout diffusion under different fault conditions. When the fault is a single narrow fissure structure, it shows a sharp pressurization type. When the fault is a large size fracture structure, it shows a slow pressurization type. When the fault is a combination of several fractures with poor connectivity, it is a wave booster type.