This study presents a 3D rough fracture grouting model on an engineering scale, specifically investigating the diffusion mechanism of slurry under different fracture surface roughness, openness, grouting pressure, fracture inclination, and slurry viscosity in fractured rock bodies. Using the software COMSOL Multiphysics, the study examines the slurry flow law within the fractures. It is observed that the profile of the slurry diffusion surface is influenced by the roughness of the fracture surface. A rough fracture surface hinders slurry diffusion and is a key cause of anisotropy in slurry diffusion. Furthermore, a quadratic polynomial relationship is identified between the grouting rate and the degree of opening. Large fracture opening results in smaller losses in grouting rate. Injection pressure is found to weakly affect the slurry diffusion profile, mainly changing the diffusion radius of the slurry. There is a positive correlation between injection pressure and diffusion radius, with a quadratic polynomial relationship with injection rate. Higher injection pressure leads to lower loss in injection rate. The effect of slurry viscosity on the slurry diffusion pattern depends on the range of viscosities, primarily changing the range of slurry diffusion. This study sheds light on the slurry diffusion pattern in rough fissures and provides a theoretical basis for grouting prediction and management in extraction area.