Abstract: In order to evaluate the quality of the synchronous grouting of shield construction and to propose parameter regulation means for grouting optimization, taking the coastal sandy soil stratum as the target, the shield synchronous grouting model test was designed and carried out to obtain the slurry diffusion law at various locations on the outside of the tunnel. On the basis of calibrating the contact parameters between particles in the discrete element model with the help of test results, a continuous-discrete element coupling model of the shield synchronous grouting was established to simulate the process of filling and penetration of the slurry, and analyze the main reasons leading to the difference in the thickness of the slurry layer in comparison with the test results, and then optimize the filling effect of the slurry layer by adjusting the grouting parameters. The results show that the particle migration characteristics of the discrete element simulation model can effectively show the filling and permeation phenomena of slurry in the excavation gap and the surrounding soil layer; affected by the mobility, the slurry is easy to gather in the grouting hole, and if the grouting pressure is insufficient, it will lead to poor homogeneity of the slurry layer on the upper and lower sides of the tunnel which are far away from the grouting hole; the filling effect can be effectively improved by adjusting the pressure difference between the grouting holes of the shield machine; affected by the pressure of the soil layer, the thickness of the slurry layer on the upper side of the tunnel is relatively thin compared to the lower side, and the slurry at the lateral side of the tunnel will deposit under the action of its own gravity, and shows a distribution of thin on the upper part and thick on the lower part.