Abstract: In view of the problems of low surrounding rock strength and serious roof falling during driving in three-soft coal seam, pre-grouting in driving face is adopted to control roof fall. According to Darcy's law and infiltration grouting theory about the diffusion law of established slurry in coal, the permeability coefficient, porosity and hydrodynamic parameters of the slurry in Zhaojiazhai coal mine were determined in the test. On the basis of these parameters, the numerical simulation experiment was used to reveal the change of pore pressure distribution and saturation around the grouting hole, and the effect of different stress states on the slurry diffusion in the driving face was analyzed. Compared with the distribution curves of pore pressure and saturation around the grouting hole under different grouting pressure and according to the degree distribution curve, it was found that the stress state has little effect on the maximum diffusion radius of slurry. Combining theoretical calculation and numerical simulation results, the grouting volume was determined to be 0.06 m3/min, and the grouting pressure was determined to be 2.5 MPa, which was close to the numerical simulation calculation results, so the diffusion radius was determined to be 1.4 m, and this result was applied to the Zhaojiazhai coal mine roadway development construction site, the grouting effect was checked by drilling cores, and it was found that the slurry diffusion was in good agreement with the expected results.