Abstract: In order to improve the bearing capacity of soft soil, a new-style composite pile has been used in the project. The new-style composite pile is obtained by inserting a precast concrete pile into a cement-mixing pile. As a new pile, although it is applied in practical engineering and its bearing capacity is higher than the design value, the microscopic study on stress characteristics of the pile is less, and the theory is not perfect yet. How to calculate the ratio of horizontal resistance coefficient of foundation soil with composite piles, there is no corresponding regulations and instructions in norms. To study the bearing capacity of the composite pile under lateral loading, the lateral loading tests on three composite piles are carried out. Through calc ulation and analysis it is explored how to calculate the ratio of horizontal resistance coefficient of foundation soil with composite piles. Experiments show that the design value of horizontal bearing capacity and the corresponding deformation should be used to calculate of the <>m value of the pile; Flexural rigidity of the pile <>EI can take algebraic sum of core pile and mixing pile. The <>m value of the pile is close to that of the filling pile in the Chinese Technical Code for Building Pile Foundations.