Grouting behind the wall is the best means to control the water burst, in coal mine vertical shaft, and the main grouting object is the fracture in wall rock. In order to study the slurry diffusion rule, according to Newton''s law of friction resistance and the force''s balance rule, the paper derived the model of fracture''s grouting in dynamic water. Through analyzing the influence of flow on slurry diffusion, respectively concluded the slurry diffusion model in the flow and contrary directions. From the model we can know that the flow direction is helpful to improve the grouting effect, The influence degree of contrary water flow on the radius of slurry diffusion is bigger than that of the flow direction. Obtained the relationship between the slurry diffusion radius and grouting pressure and the slurry diffusion radius with grouting time under the condition of different direction of flow.