Abstract: With the increasing depth of coal resource extraction, fault fracture zones, characterized by well-developed fractures, loose structures, and weak cementation, are prone to evolve into water-conducting channels under the coupled effects of mining-induced disturbance and confined water pressure. These zones have become critical influencing factors for water inrush hazards in deep mines. Grouting reinforcement is an essential technique to enhance the water-resisting capacity of fault zones; however, the diffusion of grout within the complex fracture networks of fault fracture zones and the associated permeability evolution mechanisms remain insufficiently understood. Under multiphase flow coupling, the dynamic coupling among time-dependent grout viscosity, particle deposition, and fracture heterogeneity has not been effectively characterized. It aims to establish a coupled theoretical model for grout flow in water-conducting fault fracture zones, capturing the entire process of slurry diffusion, sedimentation, and pore blockage, and to employ multiphysics numerical simulations to explore the effects of grouting parameters on slurry diffusion behavior and permeability evolution. Based on Warren-Root model, a grouting diffusion model of the fractured zone of water-conducting fault is established by coupling the slurry flow equation, the migration and deposition mass conservation equation and the permeability evolution equation, which depicts the dynamic coupling process of slurry diffusion, solidification, particle deposition pore plugging and fault permeability change during grouting. Taking Yuandian No.2 coal mine grouting project as an example, the study on the diffusion law of grouting slurry in the fractured zone of water-conducting fault is carried out, and the influence laws of slurry water-cement ratio, grouting pressure and grouting section length on the diffusion distance, diffusion area and fault permeability are analyzed, and the key influencing factors for water-blocking efficiency were identified using range analysis. The results show that the slurry diffuses in an elliptical shape along the fault dip angle, and the diffusion distance and area of the slurry undergo two processes: rapid growth and gradual stability. After grouting reinforcement, the permeability coefficient of the fault appears two stages: rapid decline and stability, and the reinforcement effect of the fault near the grouting hole is good, but the reinforcement effect at the position of the slurry diffusion front is not obvious, and the permeability coefficient changes little. Grout diffusion distance and permeability are most significantly influenced by grouting pressure, while the grout diffusion area is most significantly affected by the length of the grouting section. When the grouting parameters are water cement ratio =3∶1, grouting pressure =20 MPa and grouting section length =20 m, the distance and area of slurry diffusion along the fault reach the maximum value, and the permeability coefficient reaches the minimum value. The research results provide theoretical support and engineering guidance for mine fault water disaster prevention and control.