Dynamic failures of rock masses under strong ground motion are common phenomena usually observed but lack of studies because of their complexity. Deformation failures of layered rock masses under strong ground motion are studied by physical simulation experiments. Horizontal ground motion with different amplitudes and frequencies is respectively operated on models with different structure characteristics to investigate dynamic failure of layered rock masses according to mutual relation between discontinuity orientations and seismic forces. The results indicate that deformation failures of rock masses have different forms and distributing characteristics because of different spatial relations between discontinuities & dynamic forces and different discontinuities strengths. Structure failure of rock mass is principal that can be classified into macroscopical failure and microcosmic damage

structure characteristics of rock mass is dominating factor of dynamic failure of rock mass; inhomogeneity is one of its outstanding characteristics that are similar with those of the rock mass suffered from strong ground motions at meizoseismal areas. More researches are badly needed to establish dynamic failure modes of rock mass and to carry out quantitative mechanical analysis.