Abstract: In order to improve the wetting radius and effect of coal seam water injection, based on the actual situation of a mine driving face of kailuan Group, we simulate the wetting radius under different influcing factors during the water injection process by Fluent software and porous medium model. The results show that wetting radius is 1.82 m under the existing conditions of coal seam injection; wetting radius increases about 0.15 m when the injection pressure increases 2 MPa; wetting radius increases about 0.1 m when the injection length increases 1.5 m. The moisture content of coal seam increases 1.39% and dust concentration decreases 21% on average after optimizing the injection process according to the result of simulation. So we can increase injection effect to reduce the dust concentration of driving face by increasing the injection pressure and hole length.