To further investigate the mechanical characteristics of overconsolidated unsaturated cohesive soil and to verify the proposed three-shear subloading surface model for overconsolidated unsaturated cohesive soil through true triaxial numerical tests, Jiangxi laterite was selected as the research object. Using PFC3D software and based on the Hill contact model, conventional triaxial and true triaxial test models for overconsolidated unsaturated cohesive soil under flexible membrane conditions were established. Particle flow numerical simulations were conducted for static and dynamic cyclic triaxial tests under varying matric suctions, overconsolidation degrees, and stress amplitudes to obtain the evolution laws of macroscopic mechanical characteristics such as the stress-strain relationship of overconsolidated unsaturated cohesive soil specimens, and to analyze the evolution of contact force chains and displacement fields during shearing from a mesoscopic perspective. The PFC3D numerical simulation results were compared and validated against the results of conventional static and dynamic triaxial consolidation-drained tests on overconsolidated unsaturated cohesive soil. The results demonstrate that the simulation values from the particle flow software are consistent with the experimental results and can satisfactorily reflect the mechanical characteristics of overconsolidated unsaturated cohesive soil, including strain softening, dilatancy, as well as the ratcheting effect and Masing effect under dynamic loading conditions. The applicability of the particle flow model computational program in simulating the basic mechanical characteristics such as stress-strain behavior of overconsolidated unsaturated cohesive soil was verified, achieving a level suitable for conducting numerical experiments, which indicates that the established particle flow model can replace laboratory tests for overconsolidated unsaturated cohesive soil under various complex loading conditions. Employing the particle flow model as a digital testing machine to substitute for laboratory true triaxial tests, the theoretical results of the three-shear subloading surface model for overconsolidated unsaturated cohesive soil were verified. The results show that the constitutive theoretical calculation results exhibit essentially the same trend as the PFC3D numerical simulation results. The Fredlund stress variable approach is closer to the PFC3D simulation results compared to the Bishop stress variable approach, with smaller errors.