Relying on a proposed foundation pit project in Lanzhou City, considering the nonlinear synergy of soil and supporting structure deformation and the continuous deformation of soil, a numerical model was established by PLAXIS 3D finite element analysis software, and the whole process of foundation pit excavation was numerically carried out. Simulation, according to the simulation results, the deformation and stress of the existing tunnel caused by the excavation of the foundation pit are analyzed, and the safety evaluation of the support project is carried out. The results show that the foundation pit support scheme is feasible, and the influence of the foundation pit excavation on the existing tunnel is within the controllable range; the foundation pit excavation causes the sliding deformation of the soil around the foundation pit to present an arc shape, and the soil body deforms into an elliptical circle. The arc surface distribution, the deformation range of the soil around the foundation pit is 2~3 times of the excavation depth of the foundation pit; during the excavation process of the foundation pit, the maximum horizontal displacement of the pile body will move down with the excavation of the foundation pit, and in the process of excavation of the foundation pit The depth of the foundation pit increases the most at 1/3~2/3, and the maximum displacement is reached when the excavation reaches the bottom of the pit; the deformation of the tunnel is mainly the uplift value in the lower part of the foundation pit. It is dominated by horizontal deformation. During the excavation of the foundation pit, the supporting structure, the soil and the tunnel will undergo continuous deformation reaction. The closer the excavation depth is to the tunnel, the more obvious the deformation will be.