Abstract: Grouting filling is the key technology to solve the large-scale collapse of large and high goaf under water filling conditions.The law of slurry diffusion is of great significance for engineering design.The influence of water cement ratio, particle size of injection medium and grouting pressure on slurry diffusion radius and pressure stability value was studied by orthogonal test method, and the variation law of slurry diffusion shape and slurry pressure was discussed in depth.The results show that the influence of each factor on the diffusion radius of the slurry is in the following order: the particle size of the injection medium, the water-cement ratio and the grouting pressure.The particle size of the injection medium has a significant effect on the diffusion radius of the slurry.The influence of various factors on the stable value of slurry pressure is water-cement ratio, particle size of the injection medium and grouting pressure in turn, among which water-cement ratio and particle size of the injection medium have significant influence on the stable value of slurry pressure.During the grouting process, the slurry flow experienced three stages: vertical settlement, lateral diffusion and upward penetration.The overall pressure change shows the dynamic characteristics of dynamic peak, drainage pressure relief, step-by-step growth and stabilization.The results can provide reference for grouting filling design.