The riparian zone of the Three Gorges Reservoir undergoes high-pressure water submergence and alternate wet-dry condition, leading to changes in soil mechanical properties, influencing soil erodibility and bank instability. Based on the wide distribution of purple soil in the Three Gorges Reservoir, we simulated the hydraulic effect and the process of alternate submergence and exposure, researched stress-strain and shear strength of purple soil in response to high-pressure water submergence and wet-dry cycles. It was found that water column pressure, and the frequency and magnitude of wet-dry cycles significantly drove the changes in soil mechanical properties. Compared with CK, stiffness increased, the decreasing rate of cohesion (c) became slower, but the internal fraction angle (φ) increased with increasing water column pressure. With the increasing number of wet-dry cycles, stiffness and cohension decreased, while the internal fraction angle increased. The shear strength decreased quickly with increasing amplitude of wet-dry cycles under the same confining pressure. Compared with CK, the purple soil which suffered minor amplitude of wet-dry cycles showed a significant increasing trend in the internal fraction angle and a decreasing trend in cohesion.