<p>There is still a lack of understanding of the response mechanism of root piles under horizontal loading. The present analytical model is established based on the matrix transfer method to study the stress and deformation characteristics of root piles under horizontal load, in which the influences of root squeezing effect, pile-soil friction effect are considered, and the effective length of the root in semi-infinite space soil is studied. A response program was written on the MATLAB platform to obtain the deformation and mechanical response of the root pile. The feasibility and reliability of the theoretical method were verified by experimental cases of root piles, even in the stage of large deformation. The presence of roots significantly improves the horizontal bearing capacity of root piles in a parametric study based on this numerical case. It is shown that horizontal bearing capacity of root pile rises with increasing position of roots and increasing modulus of soil. There should be a range of root length, as the lateral bearing capacity of root piles does not increase with increasing root length.</p>