cemented paste backfills (cpb, comprising waste tailings, hydraulic binder, and water) are essential for safe and efficient underground mining production. once delivered into underground excavations, cpb undergoes complex field conditions. maintaining the engineering performance and mechanical stability of mine backfill mass, including fibers, can significantly enhance its mechanical behaviors (especially post-peak resistance) and cpb properties. nevertheless, the field loading conditions are commonly featured in various loading rates. therefore, to ensure backfill mass stability, it is essential to fully understand the effect of displacement rates on the mechanical behaviors and properties of fiber-reinforced-cpb (fr-cpb). this study examined the effect of different displacement rates (0.2mm/min, 1mm/min, 5mm/min, and 10mm/min) on the fracture behavior and properties of fr-cpb, which were prepared with three polypropylene fiber lengths (6mm, 13mm, and 19mm), and four fiber content (0.25%, 0.5%, 1%, and 1.5%) at three different curing times (7 days, 28 days, and 90 days). a comprehensive testing program was designed and performed, including semi-circular bend tests, end-notched disc bend tests, and sem observations. the results demonstrate that load-displacement curves are sensitive to the changes in the displacement rate, with a higher displacement rate resulting in a higher peak load and post-peak resistance load. moreover, it was also found that, compared with the influence of fiber content, the fiber length variation can interfere with the displacement-rate dependency of fracture properties to a greater extent. furthermore, it is interesting to observe that excessive usage of fibers can cause material stiffness, fracture toughness, and fracture energy degradation. loading rate (1mm/min) has been identified, which can cause significant changes in the rate of change in fracture properties. in terms of optimum usage of fibers, the results show that a fiber length of 13mm and a fiber content of 0.5% can maximize the fiber reinforcement effect on the improvement of fracture properties of cpb under different displacement rates. therefore, the findings from this study can potentially promote the successful implementation of fiber reinforcement techniques in the mine backfill operation.