Abstract: The complexity of the material composition of debris avalanches results in the impact effect on engineering structures not being completely understood. In particular, how particle size and distribution characteristics affect the impact force and its composition and how to consider the influence of particle size characteristics in the design of barrier structures still lack in-depth research. To answer these questions, this paper has conducted a series of centrifuge modeling tests and DEM simulation tests. The results indicate that the particle size dominates the fluctuation behavior of the impact force of the debris avalanche, and with increasing particle size, the peaks become increasingly obvious, accompanied by a significant discrete impact force. Smaller particles show an obvious cushion-effect to larger particles, and smaller particles more easily enter into the void formed by larger particles and interact with the barrier, thus contributing to the total impact force. Therefore, both the particle size and distribution characteristics control the absolute value of the impact force. The particle characteristics determine the momentum transfer mechanism at the particle scale and thus the impact effect. For this reason, we find that the dynamic impact pressure coefficient shows an increasing trend with increasing Savage number of debris avalanches, and thus, we suggest that the Froude number and Savage number should be jointly used to select appropriate . In addition, based on the analysis of the acting point of the resultant impact force, we suggest that in engineering design, the total impact force combined with the rectangular distribution mode can be adopted for safety.