Abstract: The water level in the Three Gorges Reservoir fluctuates periodically between 145.00 m and 175.00 m.Due to this cyclical variation, the rock mass on the reservoir bank slopes is repeatedly subjected to alternating dry and wet conditions, resulting in the formation of a substantial vertical water-level fluctuation zone approximately 30 m in height.The continuous action of water has led to the degradation of the bank slopes within this zone, accelerating the deterioration of the rock mass structure, amplifying deformation, and reducing overall strength.This effect is particularly pronounced in the Jurassic strata, which are known as the slippery strata in the Three Gorges Reservoir area.In this study, the Zigui Basin within the Three Gorges Reservoir area is selected as the research region.Based on field engineering geological surveys, Jurassic argillaceous siltstone is chosen as the research object.Experiments are conducted to simulate degradation under both cyclic wetting-drying conditions and long-term immersion.Through laboratory testing and theoretical analysis, the deterioration patterns of the shear properties of the structural planes in argillaceous siltstone are investigated, and a model for the degradation of shear strength under hydro-mechanical interaction is established.The results indicate that frequent and rapid wetting-drying cycles significantly contribute to mass loss in argillaceous siltstone, although water-rock interaction has limited influence on the morphology of rock discontinuities.Under the three degradation conditions, cyclic wetting-drying, long-term immersion, and their combined effect, the reduction in shear strength of the structural plane is governed by both roughness and normal stress.The magnitude of strength degradation increases progressively with higher roughness and normal stress.Moreover, under combined wetting-drying cycles and long-term immersion, the cyclic process exerts a more pronounced deterioration effect on rock discontinuities.The resulting degradation in shear strength is not a simple superposition of the two effects; instead, it involves a complex coupling mechanism.This research provides a theoretical and practical foundation for stability analysis of rock slopes and contributes to the understanding of water-induced deterioration patterns in rock mass structural planes within the Three Gorges Reservoir area.