Abstract: The purpose of this paper is to determine the relationship between macro and micro mechanical parameters of particle flow in unsaturated purple soil. We use three-dimensional particle flow software(PFC^3D),combine the control variable method and Mohr-Coulomb failure criterion,and carry out numerical simulations of triaxial consolidation and undrained tests of unsaturated purple soils under different water contents(8%、10%、12%、14%、16%、18%) and confining pressure conditions(100kPa、200kPa、300kPa、400kPa). We compare with the indoor lab test results. The results show that the cohesion of remolded purple soil first increases and then decreases with the increase of water content,and there is a critical water content of 12%. The internal friction angle is negatively correlated with water content. The macroscopic strength parameter cohesion of the purple soil is linearly positively correlated with the microscopic parameter tangential bond strength. The value of the internal friction angle is determined by the particle tangential bonding strength and the friction coefficient. The quantitative relationship between the water content of the purple soil and the shear bond strength and friction coefficient is established. The changes of cohesion and internal friction angle of purple soil under different water content are simulated by changing the shear bond strength and friction coefficient. The correctness of the relationship is verified by comparing the stress-strain curve of numerical simulation with that of laboratory test. The movement of triaxial micro particles and the distribution characteristics of indirect contact force of particles in purple soil can be observed by using the slicing tool built in PFC^3D. It provides a reference for further study on shear strength characteristics and stress-strain characteristics of purple soil.