A three-dimensional discrete particle simulation method was used to simulate the movement of debris landslides composed of four different types of debris particles. The effects of particle size on the movement characteristics of rock debris landslides were studied. The results show that the particle size distribution of debris particles has no effect on the total movement time of rock debris landslide and the moment of reaching the maximum velocity. The composition of debris particle size has a great influence on the landslide moving velocity, destructive force and sliding distance. The more inhomogeneous the particle size distribution is, the greater the velocity and destructiveness of landslide and the longer the sliding distance is. The leading edge of the debris flow source is the controlling factor for the magnitude of the impact of the landslide-debris flow hazard. The research results can provide reference for the prediction and evaluation of rock debris landslide disasters in the future.