Mechanical characteristics of cementitious materials with fiber reinforcement are different from non reinforced cementitious materials. The influence of fiber type and content, solid content, and cement to-tailings ratio (c/t) on crack resistance and post-peak toughness of cemented tailings backfill composites (CTBC) was explored in this study through the three-point bending experiment of an orthogonal design scheme. A numerical model was also established to reveal the crack propagation mechanism and evolution law of the fiber reinforced CTBC beam. Results show that CTBC & rsquo;s bending strength is greatly affected by the solid content and c/t factors. When compared to polyacrylonitrile, glass and polyvinyl alcohol fibers, polypropylene fiber (PP) has the best reinforcement effect. Secondly, the deflection of the CTBC reinforced with fibers is higher than peak deflection, and the influence of four factors on CTBC & rsquo;s post-peak toughness is as follows: fiber type > fiber content > c/t > solid content. The fitting model of the load & ndash;deflection curve combined with quadratic polynomial regression has good reliability, guessing CTBC & rsquo;s load & ndash;deflection curve based on the fiber reinforcement effect. Incorporation of fibers reduces the particle velocity in the cementitious material model and delays the crack propagation stage after peak load, and its tensile stress is most significant at peak load. The data gained from this study will contribute to both structural and operational design of the CTBC used in underground metal mines for sustainable mining and backfilling operations.