This study employed a low–speed drop–hammer–impact test combined with the digital image correlation technique to investigate the dynamic failure performance of bamboo fiber/high–density polyethylene (BPE) composites and to explore the mechanism of fiber content’s influence on it. Results indicated that with the increasing of BF content, the density, acoustic velocity, and Poisson’s ratio of BPE gradually decreased, while the elastic modulus initially decreased and then increased. Although the introduction of Bamboo Fiber (BF) enhanced the rigidity of BPE, allowing the materials to withstand greater impact forces during initial fracture stages, it reduced the toughness of BPE. BPE with 80% BF content showed a higher crack propagation rate and a shorter fracture process compared to composites with lower BF content. However, according to the stress intensity factor (SIF) history, the introduction of BF could enhance the resistance of crack propagation, which depends on the dispersibility of BF and the interfacial bonding properties between BF and high–density polyethylene (HDPE). Overall, BF could increase the rigidity of BPE and restrict the crack propagation at the initial fracture stages. As an eco-friendly and sustainable material, the dynamic fracture toughness of BPE can contribute to the application and promotion of biomass fiber-filled composites.