Abstract: Because of the complexity of ambience and the construction of city subway, foundation pit excavation can cause disturbance to the soil, and bring damages to the buildings and underground pipes, even the stability of foundation pit can be lost. Based on the project of a deep pit,with the aid of FLAC^3D, established the foundation pit excavation calculation model. The results showed that the calculation model can simulate the actual excavation process. By the change of model parameters, The author Summarized the influence of the retaining piles stiffness,the retaining system force and deformation, and drew some useful conclusions, and ensured the city deep foundation pit excavation and retaining structure security.