Abstract: To investigate the mechanism of grout spreading in jointed rocks, a numerical model for simulating planar fracture grouting is developed based on the finite volume method (FVM), the volume of fluid (VOF) method, and collocated grids. This model adopts a momentum interpolation method in its calculation of the flow rate at the control volume faces to avoid the distorted solution of oscillating pressure fields, and considers the two-phase flow characteristic of grout spreading, tracking the moving interface of two phases by VOF calculations. It is tested through application to the grouting in an infinite planar fracture and the results show that its calculations of grouting pressure field distribution, flow velocity and diffusion radius agree well with the analytical solution, thereby verifying a high accuracy in the calculations and laying a basis for developing a dedicated system for fracture grouting simulation.