Abstract: In recent years, the urban infrastructure construction in China has been constantly developing. The pile foundation is a common form of foundation in infrastructure construction. The calculation of the capacity of a pile foundation is an important subject in the foundation design. Based on the Vesic expansion theory, the actual stress state of the soil on the pile side under horizontal loading is presented. A calculation method of the soil resistance on the pile side in the form of stress increment is derived, and the mechanical method of the horizontal capacity of the pile foundation considering the pile-soil interaction is proposed. The corresponding analysis program was compiled based on MATLAB software and the validity of the proposed calculation method was verified by a comparison with experimental results. The effects of the load and the pile diameter on the mechanical behavior of the pile-soil interaction system was analyzed based on the proposed mechanical model for the horizontal bearing capacity of pile foundation.