Abstract: To investigate the shear resistance performance and meso-damage mechanisms of herbaceous plant root-soil systems under freeze-thaw cycles, this study focused on wolfsbane root-soil composites. A representative three-dimensional root system model was constructed. The freeze-thaw damage process was characterized by simulating the expansion effect of water-ice particle phase transformation using the Discrete Element Method (DEM). A three-dimensional direct shear numerical model for the root-soil composite was calibrated based on indoor experimental data. The study systematically investigated the influence of freeze-thaw cycle count, shear rate, and normal load on the shear strength, damage mechanisms, and synergistic shear-resistance mechanism of the root-soil composite. The research findings revealed that:(1) The incorporation of roots significantly enhances the shear strength of the soil, with the anchoring effect of vertical roots playing a primary role. Fibrous roots can further augment the three-dimensional reinforcement effect.(2) Loading rate exhibits a positive correlation with both normal load and peak shear strength. However, its impact on the intrinsic pattern of shear strength degradation caused by freeze-thaw damage is relatively minor.(3) Freeze-thaw damage primarily manifests as the deterioration of particle bonding within the specimen, induced by volumetric changes during phase transitions in the freeze-thaw process. This leads to a reduction in interfacial forces between roots and soil during shear, thereby diminishing the soil's shear strength. The results elucidate the interaction mechanism between plant root soil reinforcement and freeze-thaw cycles. They provide a reference basis for the eco-reinforcement design of slope engineering in cold regions, offering significant engineering guidance significance, notably under extreme freeze-thaw scenarios.