Abstract: In recent years, grouting is usually applied to reinforcing surrounding rock of roadway and preventing infiltration and water plugging, but grouting technology and grouting theory has lagged behind engineering practice, especially mechanism of grout osmotic did not make substantial progress. This paper starts from the single fracture rock , the model of single fracture model is established by using numerical simulation software of COMSOL Multiphysics, the changing law of grout’s diffusion distance and seepage pressure is studying under different water cement ratio, grouting pressure,and crack opening variation degree. Some conclusions and beneficial effects have been obtained by numerical simulation, and the research results can be used to guide grouting engineering practice, and the grouting effect can be quantitatively evaluated.