With the rapid development of rail construction in China, the excavation of foundation pit above the shield section often occurs, and the large-area soil unloading will have a great impact on the existing shield section. By using finite element analysis software to calculate the excavation conditions of foundation pit, the deformation of existing sections can be analyzed and the hierarchical step sequence of foundation pit excavation can be guided. Combined with a new road frame bridge parallel to the existing subway section in Shenyang, the impact of large-area excavation of foundation pit above the section on the existing shield structure is numerically simulated by using the finite element software MIDAS GTS. The horizontal and vertical displacements of the existing shield sections are effectively controlled due to the grouting reinforcement at the bottom of the pit and the hierarchical step excavation, which provides a comparative reference for other similar foundation pit projects in China.