The grouting method has been widely adopted to improve the soft and broken ground properties in tunnelling engineering. This paper carries out numerical and experimental investigation to study the diffusion characteristics of grout in layered fault, considering the influence of flowing water and multiple injections. The fault is simplified to consist of (1) fault gouge, (2) fault breccia and (3) mixed area. It can be concluded that the grout shows significantly different diffusion characteristics in fault breccia and mixed area, moreover, due to the scouring effect of flowing water, grout has greater diffusion tendency in the direction of the water. In the case of single injection, the grout diffusion distance in mixed area was between 75.86 % and 88.10 % of that in fault breccia, while it was 59.8 % when multiple injections were carried out. It appeared that, the higher the injection pressure, the grout diffusion priority in fault breccia is greater. It can be also concluded that the pressure dissipated gradually from the injection hole to periphery, and the pressure dissipation in mixed area is faster than that in fault breccia. The results of experiment match reasonably well with numerical simulation, furthermore, the grouting reinforcement mode for layered fault medium are proposed. These conclusions can be used to better understand grouting theory.