<p>In order to clarify the relationship between mesoscopic parameters and macroscopic mechanical parameters of expansive soil and the influence of mesoscopic parameters on macroscopic mechanical properties. In this paper, taking Nanyang expansive soil as an example, the discrete element numerical model of triaxial test is established and the parameters are calibrated in combination with the indoor test results. Furthermore, the friction coefficient, porosity, stiffness ratio and minimum particle size were classified based on the orthogonal experimental design method. The results show that: (1) The discrete element numerical simulation of expansive soil established in this paper can be used to simulate the mechanical properties of Nanyang expansive soil; (2) Friction coefficient is the most significant factor affecting the deformation and strength characteristics of expansive soil, followed by porosity, while stiffness ratio and minimum particle size have no significant effect on the deformation characteristics. (3) Based on regression analysis, the relationship between macroscopic mechanical parameters and mesoscopic parameters of expansive soil is obtained.</p>