<p>Geological hazards on the Southern Chinese Loess Plateau (SCLP), particularly loess-mudstone landslides (LMLs), are increasingly triggered by extreme climatic events. This study investigates the climatic controls on the stability of the Doujitai landslide within the active Weihe Fault Zone, a representative LML in the SCLP. A series of ring shear tests were conducted on remolded loess from the landslide’s slip zone to quantify the degradation of shear strength parameters under varying water content, normal stress, shear rate, and shear modes. The results revealed that the remolded peak and residual shear strengths first increased and then decreased with increasing water content, accompanied by a transformation from strain hardening to strain softening. The remolded peak strength increased significantly with shear rate, while residual strength first decreased and then increased. Increasing shear rate also enlarged the amplitude of residual shear stress fluctuation. Compared with single-stage tests at different normal stress levels, multi-stage shear led to an attenuation of internal friction angle. Based on the experimental data, a hydro-mechanically coupled numerical analysis was conducted to model the slope’s stability evolution during rainfall. The results show an obvious relationship between the dip angle of the mudstone-loess interface and slope stability. Furthermore, the impact of rainfall intensity and duration on stability was evaluated, highlighting that higher intensity rainfall drastically accelerates stability degradation. This study elucidates the formation mechanism of LMLs under climatic control, emphasizing that extreme rainfall acts as the critical external trigger of slope instability within a tectonically preconditioned geological setting.</p>