<p>Long-term reservoir impoundment and water level fluctuations (WLFs) significantly affect the geomechanical behavior of soft-hard interbedded dip rock (SHIDR) slopes, inducing complex deformation mechanisms. In this study, a SHIDR slope from the Shuibuya Reservoir was selected as the geological prototype for constructing a reduced-scale physical model. Multi-field monitoring techniques were employed to analyze the model’s evolution, emphasizing the effects of groundwater seepage and effective stress variations on deformation, thereby revealing insights into the deformation-failure mechanisms of SHIDR slopes under long-term reservoir water influence. The results indicated that the model’s deformation process included the long-term progressive and intermittent uplift deformation stage, the accelerated deformation-failure stage, and the post-failure residual stage. The slope model exhibited local cracking, shear creep, and uneven subsidence under reservoir water influence. The reservoir water exerted a greater impact on the soft rock base than the hard rock, inducing more frequent micro-deformations and unstable stress responses. Groundwater behavior was classified into four zones based on pore water pressure during WLFs, with seepage forces influencing slope deformation and stability depending on groundwater flow direction. The slope can be classified as a hydrodynamic-driven type. Finally, initial impoundment adversely affected the slope, and the model exhibited a displacement pattern similar to the prototype as the 15 WLFs progressed. Long-term WLFs progressively reduce slope stability, with soft rock layers and pre-existing cracks crucial in failure surface formation. The evolution of SHIDR slopes follows a cataclinal-creep and compression-induced tensile fracturing pattern. These findings offer valuable insights into the deformation-failure mechanisms of similar slopes under long-term reservoir water conditions.</p>