Abstract: To study the infiltration law of grouts during grouting in irregular faults, based on the theory of self-affine fractal interpolation surface to build irregular faults and the theory of fractured rock mass grouting,the influences of fault form, grout viscosity and layout of grouting holes on the diffusion of grouts are thoroughly studied. The following results are obtained: (a) the random distribution of fault width caused by uneven surface of faults leads the grouts to noncircular diffusion, so the grouting holes cannot be arranged according to the formula for grout diffusion; (b) for the narrow faults, the grouting pressure contour of nodal interval is small, and the pressure gradient is large, and vice versa; and (c) the greater the grout viscosity is, the stronger the so called inertia of grouts is, therefore, the diffusion distance of grouts is obviously shortened. So engineers should combine the rheological tests on grouts with numerical analysis results to optimize the selection and proportion of grouts.