In view of the nonlinear mechanical properties of the fine sand formations as well as the significant geometric deformation caused by excavation of the surrounding rock structure at the arch of shield tunnels, a numerical simulation is used for the analysis of the safety of the surrounding rock structure during excavation of the arch of shield tunnels in fine sand formations to study the influence of such factors as permeability coefficient and lining thickness. The principle of grid division can be determined by adopting COMSOL Multiphysics software. According to the actual situation of shield tunnel engineering, a geometric model is constructed of the surrounding rock structure of the arch excavation of the shield tunnel, thus helping to set the soil parameters of the shield tunnel. Based on the elastic modulus parameter, the tunnel structure parameters can be calculated, with the displacement and stress changes of the shield tunnel recorded as well. The results show that during the excavation process of the arch of the shield tunnel, the maximum horizontal displacement of the tunnel is 3.5 mm, the maximum vertical displacement is 2.2 mm, and the maximum stress value is 2.9 MPa. With the lining thickness being 56 cm, the safety factor of the shield tunnel reaches as high as 9.09. The excavation of shield tunnels in fine sand formations is characterized with a relatively small impact on the surrounding rock structure. Compared with vertical displacement, the permeability coefficient exerts a greater impact on horizontal displacement, with the thickness of the lining during excavation being a potential factor affecting the safety of the surrounding rock structure.