The soil displacement caused by the foundation excavation will impose additional stresses on the pile foundations within its influence range, resulting in lateral displacement or insufficient bearing capacity of the pile foundations, which will adversely affect the pile foundations and cause uneven settlement of the structures in the long run, triggering local damage to the soil below the pile foundations and even distorting the deformation of the upper structures, affecting their safety in use. In this paper, the two-stage method is used to analyze the lateral displacement of pile foundations. The free displacement field of the soil during the excavation of the foundation pit is used as the input condition, and the lateral displacement and internal force of the monopile are solved by introducing the improved foundation reaction modulus into the Winkler foundation model. Combined with the numerical model, the effects of pit excavation on the surrounding soil, supporting structure, and adjacent pile foundations are investigated. The effects of different factors on the force and deformation pattern of pile foundations are analyzed, the degree of influence of different comprehensive stiffness of pit support on pile foundations is explored, and the comprehensive stiffness is related to the maximum horizontal displacement of pile foundations to propose a method for predicting the maximum horizontal displacement of pile foundations, which can be a reasonable reference for similar pile foundation projects.