In order to study the effect of tortuosity of diffusion paths on the grouting effect of shield tunnel segment, a penetration diffusion model of grouting through segments of shield tunnel considering tortuosity of diffusion paths was established for power-law fluid. The influence of grouting time, grouting pressure and grouting rate on the diffusion radius and the tunnel segment were analyzed. Finally, by using MATLAB and COMSOL Multiphysics software, a numerical simulation program for permeation and diffusion of power-law fluid considering tortuosity of diffusion paths was developed, and the numerical simulations of grouting for shield tunnel segment was achieved. The research results show that under the condition of other parameters unchanged, as the termination grouting pressure increases, the diffusion radius and the pressure on the tunnel segment increase. With the increasing grouting rate, the diffusion radius and the pressure on the tunnel segment first increase and then decrease. After the consideration of tortuosity of diffusion paths, the diffusion radius and the pressure on the tunnel segment decrease compared with the case without considering tortuosity of diffusion paths. With the increase of the termination grouting pressure and grouting rate, the influence of tortuosity of diffusion paths on the diffusion radius and pressure on the tunnel segment become more significant.