Unloading during double-sided foundation pit excavation can cause deformation of surrounding existing structures, and can cause collapse of the structures in more serious cases. Therefore, a double-sided foundation pit project near a subway in a soft soil area is taken as the background, the finite element software is used to establish a three-dimensional foundation pit-tunnel model, and the control variable method is used to analyze the influence of the excavation sequence of the foundation pits on both sides and the thickness of the diaphragm wall on the deformation of the foundation pit itself and the existing tunnels, and compare the numerical results with the measured results. Based on the on-site measurement, the deformation laws of tunnel segment convergence and vertical displacement at different excavation stages of foundation pit are discussed. The results show that the calculated results are in good agreement with the measured results; the alternating excavation of the two sides of the foundation pit can better control the horizontal displacement of the diaphragm wall and the horizontal and vertical deformation of the tunnel than the excavation of only one side of the foundation pit; Increasing the thickness of the diaphragm wall can effectively reduce the deformation of the diaphragm wall and the tunnel. The optimal thickness of the diaphragm wall is 1.0 m . The horizontal and vertical deformations of the existing tunnel mainly occur in the second and third stages of the construction, and the influence of foundation pit excavation unloading on the deformation of the curved section tunnel is more significant. The results can provide a certain reference for similar projects.