Grouting sealing technology in multi-branch horizontal wells has been widely used in the water hazard control of mining wells. However， the quantitative characterization method for diffusion range of grouting in the deep formation is lack of research， therefore references for space and buried depth of multi-branch horizontal wells are inadequate. Aiming at seepage grouting technology for multi-branch horizontal wells and considering the anisotropic permeability， two phase flow of cement grouting and porous water， a numerical diffusion model for seepage grouting and a theoretical model for simplified diffusion radius are built in this paper， and the numerical simulations on the seepage grouting are conducted combining with actual engineering cases. The results show that the seepage diffusion area in anisotropic formations tends to be ellipse. The major axis of ellipse is along the bedding plane which has a larger permeability， while the minor axis is perpendicular to the bedding plane. These researches provide some references for the design of space and buried depth of multi-branch horizontal wells and key parameters optimization for seepage grouting.