Abstract: Multi-layer sandwich composite structures have significant applications in impact protection. In particular, they demonstrate superior protective performance when subjected to impacts from explosive fragment particle clusters. Based on an analysis of the impact resistance and failure mechanisms of single-layer materials, this paper reviews the research progress regarding the dynamic mechanical response characteristics of composite structures under both single-particle and multi-particle impacts. The results indicate that metallic materials predominantly exhibit features such as plastic deformation, crack propagation, and localized thermal softening. By contrast, ceramics rapidly disperse impact energy due to their high hardness and propensity for brittle fracture. Meanwhile, fiber-reinforced composites achieve hierarchical energy dissipation through their continuous fiber network. Studies on multi-layer sandwich structures show that high-speed particle impacts on the target plate have been found to induce phenomena such as localized stress wave propagation, micro-crack formation, and interfacial delamination. The mechanisms underlying impact resistance in these structures are complex. However, current research primarily focuses on the impact resistance of structures under single-impact conditions. The protective mechanisms under multi-particle impacts remain unclear, and the employed research methods are relatively limited. Experimentally, approaches such as the modified split Hopkinson pressure bar (SHPB) apparatus are predominantly utilized to achieve high-speed loading of particle clusters. Nevertheless, issues regarding secondary impacts and velocity limitations in these experiments have yet to be effectively resolved. In numerical simulations, the smoothed particle hydrodynamics–finite element method (SPH-FEM) coupling approach remains the mainstream method for investigating particle cluster impacts. However, concerns regarding the accuracy of these models still warrant further investigation.