A novel hierarchical multiscale strength reduction method with a coupled finite element method (FEM) and discrete element method (DEM) approach is proposed for a heterogeneous slope. This approach is implemented and validated by employing a soil and rock mixture (SRM) slope. Compared with conventional strength reduction method, this method avoids the expensive cost of large field tests in parameters estimation and provides a better understanding of the failure mechanism with macroscopic and microscopic results. The multiscale simulation approach, which is directly based on particle-level simulation and bypasses conventional constitutive assumptions, provides a novel numerical tool for slope stability analysis of heterogeneous geomaterials.