<p>The degradation mechanism of interparticle cementation in frozen clay is complex and difficult to quantify during testing. Consequently, empirical formulae capturing this cementation degradation are commonly used in constitutive modeling. In this study, the discrete element method (DEM) is used to monitor the interparticle bond state in frozen clay during loading, and a microscopic damage factor is proposed to quantify the degradation of interparticle bonding. Meanwhile, low-temperature triaxial tests and isotropic loading–unloading tests are conducted on frozen clay under different cooling temperatures and confining pressures to obtain its macroscopic mechanical characteristics. Based on these studies, an elastoplastic constitutive model that accounts for micromechanical damage is developed on the basis of the primary Unified Hardening (UH) model. The microscopic damage factor is introduced into the tensile strength term for frozen clay, and the incremental form of the stress–strain relation is derived within elastoplastic theory. The meanings and identification methods of the required model parameters are provided. Comparisons with experimental data demonstrate that the model accurately predicts the stress–strain response and volumetric deformation under a wide range of cooling temperatures and confining pressures.</p>