Abstract: This paper aims to address the problem that the long-term mechanism of grouting treatment for large transverse deformation of shield tunnels is still unclear. Based on the case of grouting treatment for the Shanghai metros and taking into considertation the coupling effect of water and soil, numerical simulations of different grouting methods are conducted by using the virtual swelling stress method. The study reveals the dissipation mechanism of excess pore water pressure and the deformation mechanism of the tunnel during the consolidation stage and unveils the patterns in the effects of excess pore water pressure dissipation on the long-term efficiency of grouting. It is found that the dissipation of excess pore water pressure could be divided into two modes: the diffusion of local excess pore pressure and the drop of the overall excess pore pressure, and different dissipation modes will have different effects on the tunnel deformation. The recovery of transverse deformation of the tunnel is relatively stable at the early stage of consolidation, and as the excess pore water pressure decreases, such recovery will enter a rapidly rebounding stage after 10~30 days of consolidation, and gradually decelerate to stability after about 100 days. The distribution pattern of the excess pore water pressure caused by grouting is the most significant factor that affects the long-term efficiency of grouting. Therefore, improving the grouting method as a way to improve the distribution of excess pore water pressure generated by grouting can effectively improve the long-term effect of grouting treatment for transverse tunnel deformation.