The sequential relationship between earthquakes and rainfall significantly influences slope stability. To elucidate the influence mechanism of dynamic responses and deformation and failure of slope under rainfall-earthquake sequential effects, we carried out hollow cylindrical torsion tests of 12 groups of sandy clay samples and attempted to analyze the variation rules of shear stress and volumetric strain of these samples with axial strain under rainfall-earthquake sequential effects. It was observed that the sequential effects significantly influenced the ultimate shear stress of sandy clay, especially under post-seismic rainfall conditions. Volumetric strain showed negative directional and negative frictional behaviors, which would affect the deformation and load-bearing capacity of soil body. Based on these observations, we mainly studied influence mechanism of dynamic responses and deformation and failure of slope under rainfall-earthquake sequential effects by taking the permanent displacement of the slope and the slip surface as quantitative evaluation indicators of dynamic damage and failure of the slope. The results showed that the presence or absence of seismic damage before rainfall could greatly affect the rising speed of underground water level inside the slope, which would lead to various deformational failure modes. The results also showed that the damage of slopes vary with earthquakes of different magnitudes, and hence the shape, scale, and shear exit location of the slip surface vary as well during subsequent rainfall. However, the damage is generally showed as tension cracks at a certain height on the slope. With sustained rainfall, these cracks gradually extend downwards the base of the slope, leading to sliding failures and eventually resulting in accumulation body at the base. The findings could provide theoretical and technical support for slope stability assessment and protection in analogous engineering problems.