Soil rock mixture (SRM) is a special geological material with non-uniform rock distribution, non-continuous cementation between rock and soil, and size effect structural characteristics, hence, possessing mechanical properties different from rock or soil. Field survey indicated that the surface layer of SRM above the rock slope was almost unstable under cyclic loading; however, at the same time, the slope itself was stable. This phenomenon exceeded initial judgments, thus it was important to study the mechanical characteristics of SRM under cyclic loading. Numerical simulation using continuum-based discrete element method was employed to study the strength degradation and failure mechanism of SRM under different frequencies, dynamic stress amplitudes and durations. Results show that the peak stress gradually increased with the increasing dynamic stress amplitude and frequency, but decreased with the increasing percentage of rock because the stiffness decreased greatly under cyclic loading. At the same time, the elasticity modulus decreased gradually with the dynamic stress amplitude and increasing frequency.