Abstract: When a single-pile foundation is subjected to horizontal loads, the vertical friction resulting from the cross-sectional rotation of the pile develops into an additional resistance moment from the soil to the pile, and the soil at the pile tip also forms a certain additional resistance on the pile. To explore the influence of the additional resistance of the pile and pile tip on the horizontal bearing features of the single pile, deduces the discrete numerical solution and simplified formula solution of additional moment based on the friction model of sand recommended by the API code in combination with the ultimate friction enhancement effect caused by the radial soil pressure. Also adopts the friction model of clay recommended by the API code to deduce the discrete numerical solution and simplified formula solution of the additional moment in the cohesive soil. Based on the hyperbolic stress-displacement model and the separation effect of pile-soil interface, deduces the discrete numerical solution and simplified formula solution for the pile tip additional moment and the discrete numerical solution of pile tip horizontal shear force. Furthermore, proposes a finite element method based on the Winkler foundation beam model and compiles a program. By comparing with the experimental data, the correctness of the method adopted in this paper is verified. The parameters of the horizontal bearing capacity are analyzed. The results show that, as the ratio of pile length to diameter increases, the proportion of additional resistance in the total horizontal bearing capacity gradually decreases, while the proportion of additional resistance in the total horizontal bearing capacity shows no significant changes as the pile diameter increases.