Abstract: The slip zone soil plays an important role in controlling the deformation and evolution of landslides. It is of great significance to study the strength characteristics of slip zone soils under different seepage conditions for the dynamic stability evaluation of reservoir accumulation landslides. In view of the current weak researches on the seepage-mechanical properties of soils of reservoir accumulation landslides, the Tongjiaping landslide slip zone soil in the Three Gorges Reservoir area is taken as an example to study the residual strength characteristics based on the ring shear tests under different seepage conditions. The ARS ring shear apparatus and the self-developed coupling devices for seepage-ring shear are employed to operate different shear modes of cyclic seepage pressure on the strength variation characteristics of the slip zone soil. The experimental results indicate that the phenomenon of 'strain softening' easily appears, meanwhile, it is promoted by the increase of seepage cycle. Additionally, the seepage cycle significantly weakens the cohesion of the slip zone soil. Moreover, under the same shear stress condition, the change trend of the shear stress under the action of seepage is basically the same, however, the residual strength is negatively correlated with the seepage pressure. The research results reveal the weakening laws of mechanical strength of the sliding zone soil under seepage cycle, which provides a basis for the studies on the mechanical mechanism of accumulation landslides under reservoir operation.