<p>Following the impoundment of the Three Gorges Reservoir, the reservoir fluctuations, whether gradual or rapid, expose the soil and rock mass within the slip zone to prolonged drying-wetting cycles (D-W cycles), which directly influence the mechanical parameters responsible for landslides’ deformation and stability. As an illustration of this phenomenon, the Shilongmen landslide serves as a case study. Taking into account the impact of both D-W cycles and the overlying load on the soil, a strength degradation model for the slip zone soil is established. This model is employed to analyze how the deformation and stability of the Shilongmen landslide change under the prolonged cyclic influence of reservoir water. And the SLOPE/W software with custom secondary development is utilized for this analysis. The findings indicate that the presence of an overlying load during D-W cycles acts as an inhibiting factor for degradation, and higher loads result in more pronounced inhibition. Taking into consideration the degradation of soil parameters within the slip zone under the prolonged influence of reservoir water cycles, the overall stability factor of the landslide demonstrates a distinct deteriorating trend. Deformation within the landslide predominantly manifests in the middle and rear sections, along with the surface area of the front edge. This observation aligns with the documented emergence of cracks and subsidence in the field investigation. These research findings offer valuable insights for assessing the long-term stability of landslides in reservoir conditions. Additionally, the analytical methods utilized here can serve as a valuable reference for similar experiments.</p>