The shield tail synchronous grouting area is located behind the shield tunnel segment wall. Due to its closed space, it is difficult to directly observe the slurry diffusion, which leads to the unclear distribution characteristics of synchronous grouting materials. Therefore, a shield tail synchronous grouting simulation device was developed, and the shield tail synchronous grouting simulation test was carried out. The pressure change in the soil mass and the settlement of the upper soil mass during the synchronous grouting process were studied. The results show that the pressure in the soil above the moving axis of the grout outlet gradually increases under the influence of the grouting pressure after the grouting starts, and gradually decreases after the grout outlet is far away. At the same time, the soil pressure on both sides of the axis gradually increases, resulting in an obvious soil arching effect; The internal pressure of grout after grouting stability is mainly determined by the upper load,which has no direct relationship with the grouting pressure in the grouting stage; The surface settlement caused by grouting is mainly determined by the grouting pressure, and secondly affected by the slurry property; The thickness of solidified grouting body is smaller in the transverse direction near the grout outlet, larger on both sides, and the thickness distribution is more uniform in the longitudinal direction.