With the continuous advancement of urban construction, underground engineering has entered a period of rapid development. Foundation pit engineering will inevitably have an impact on the surrounding environment, especially on the existing structures. Based on the foundation pit engineering of Hongqiao Station of Nanjing Metro Line 5, this paper explored the influence of deep foundation pit excavation on its own retaining structure, surrounding ground surface, and adjacent existing municipal tunnels through on-site construction monitoring and numerical simulation. The results show that the excavation of the foundation pit results in a large settlement of the surrounding ground surface, and the maximum settlement position is about 0.35 the excavation depth from the foundation pit. The horizontal displacement of the diaphragm wall first increases and then decreases with the depth, reaching the peak value at the depth of 15–16 m. The maximum horizontal displacement at the end well is less than that at the standard section but does not exceed the limit value. When excavation proceeds to the pit bottom, the axial force of the third support is the largest, which is close to the location where the maximum deformation of the diaphragm wall occurs. The north side of the tunnel structure close to the foundation pit has a vertical uplift, and the horizontal direction has a small displacement towards the pit.