Abstract: Secant piles are more and more widely used in China. In order to clarify the stress characteristics of the reinforced concrete piles and plain concrete piles in secant piles, study concerning various pile diameters was performed based on numerical simulation analysis. The finite element software, ABAQUS, was used to establish a numerical model, and the bearing capacity of the reinforced concrete piles and plain concrete piles was analyzed according to the simulation results, revealing the relationship between the pile diameter and the mechanical characteristics of the reinforced concrete piles and plain concrete ones. Furthermore, the contribution of plain concrete piles to the overall stiffness and bearing capacity during the working process of the secant piles was investigated. The results show that the bearing capacity of the reinforced concrete piles is better than that of plain concrete piles. With increased pile diameter, the bearing capacity of the reinforced concrete piles and plain concrete piles increases gradually. The tensile capacity of plain concrete piles is poor, but it still can improve the overall performance of the secant piles and contribute greatly to the overall stiffness. The research results are of important engineering significance for further clarifying the influence of pile diameter on the bearing capacity and mechanical characteristics of the secant piles.