Both small and large deformations of soil and soil-rock interaction are the key features in the post-failure process of natural slopes. As one of Lagrange meshless particle methods, the Smooth Particle Hydrodynamics (SPH) method has obvious advantage in dealing with the large deformation and interface interaction problems. Thus in this paper, the SPH method is employed to study the slope failure problems, especially focusing on soil large deformation and soil-rock interaction in natural slopes constituted of earth-rock aggregate. The Drucker-Prager model is implemented into the SPH-code to describe the elastic-plastic soil behavior while the rocks are simulated as rigid bodies by using classical rigid motion equations. The interaction between soil and rocks is modeled by the coupling condition associated with an action and reaction force between the two phases. Rock-rock contacts are computed using contact mechanics theory which is similar to the treatment in the Discrete Element Method (DEM). Two test cases including uniform non-cohesive and cohesive soil slopes failure problems are studied respectively to validate the method and a good agreement with the experimental data or numerical results is observed. Then the solution to soil-rock interaction is applied to study the behavior of earth-rock aggregate in the failure process of typical natural landslides. Numerical results show that the proposed soil-rock interaction algorithm works well in the SPH framework and has a great application potential in geotechnical engineering. Through the qualitative analysis and discussions about the behavior of earth-rock aggregate, we came to the conclusion that the soil-rock interaction has a great influence on the landslide shape in terms of rock size and slope angle. And the deformation characteristics of landslide at the slope toe is slightly different with that at the slope top.