Abstract: Deep mining of coal resources is commonly accompanied by high in-situ stress and progressive energy accumulation, which can readily trigger dynamic disasters such as rock bursts. From the perspective of toughening cemented fill materials, elucidating the impact-mitigation mechanisms of coal-based cemented fill materials and establishing an energy-dissipation-based quantitative evaluation index system are emerging as promising approaches for impact-control regulation and material-oriented design optimization. To clarify the impact-mitigation mechanisms, this study employed coal-based solid wastes as the primary constituents and systematically investigated the coupled effects of aggregate gradation, binder-aggregate ratio, curing age, and fiber toughening through uniaxial compression tests, energy evolution analysis, impact tendency assessment, and scanning electron microscopy (SEM). The results indicate that aggregate gradation, binder-aggregate ratio, and curing age exert significant influences on the mechanical performance of the cemented fill. The uniaxial compressive strength increases with curing age and exhibits a “rise-fall” trend with increasing Talbot index n and binder-aggregate ratio, reaching an optimum at 28 d with n=0.6 and a binder-aggregate ratio of 2.5:1. The incorporation of polypropylene fibers markedly enhances strength and improves post-peak deformability, broadens the energy-dissipation pathways, and enables sustained absorption and dissipation of externally imposed impact energy during the post-peak stage. Based on energy dissipation theory, a FIMI-Lite impact-mitigation evaluation framework comprising five indices—energy dissipation ratio, dynamic toughness index, residual load-bearing ratio, brittleness index, and equivalent vibration isolation coefficient—was proposed to quantitatively characterize the impact-mitigation performance of cemented fill materials. Comparative analyses show that fiber-toughened fills outperform the conventional counterparts across all indices, with the fiber-toughened fill at n=0.4 achieving the highest comprehensive FIMI-Lite score. SEM observations reveal that an appropriate gradation promotes the formation of a dense load-bearing skeleton, whereas fiber inclusion constructs a three-dimensional “particle-cementitious matrix-fiber” network; their synergy refines the pore structure, retards crack propagation, and enables stepwise energy absorption and progressive release. These microstructural findings establish a mechanistic linkage to the macroscopic impact-mitigation performance. The proposed approach provides a scientific basis for optimizing the design of coal-based cemented fill materials and for preventing and controlling coal-burst hazards in deep coal mining.