As a direct retaining structure in the process of foundation pit excavation, the internal force and deformation of pile under horizontal load have great influence on the safety and economy of foundation pit engineering. In order to calculate the internal force and deformation of the supporting pile more accurately, the nonlinear foundation reaction modulus is obtained according to the nonlinear soil resistance-pile lateral displacement (p−y) curve of pile-soil interaction. At the same time, the Pasternak two-parameter foundation model is introduced to fully consider the continuity of pile side soil deformation. The differential equation of retaining pile deflection considering pile-anchor deformation coordination is derived, and the internal force and deformation of the retaining pile are obtained by the transfer matrix method. Then the calculation program is compiled based on the engineering example, and the calculation results of the program are compared with the monitoring values and the calculation results of the p−y curve method based on the traditional Winkler foundation model. It is found that the traditional Winkler foundation model will overestimate the horizontal deformation and internal force of the retaining pile. The displacement and bending moment calculated by the program can better meet the actual requirements of the project. Furthermore, the finite element software is used for numerical simulation analysis of the engineering example to verify the rationality and applicability of the calculation method of foundation pit supporting piles based on the nonlinear Pasternak two-parameter foundation model.