Abstract: Cemented tailings backfill (CTB) not only boosts mining safety and cuts surface environmental pollution but also recovers ores previously retained as pillars, thereby improving resource utilization. The use of alternative reinforcing products, such as steel fiber (SF), has continuously strengthened CTB into SFCTB. This approach prevents strength decreases over time and reinforces its long-term durability, especially when mining ore in adjacent underground stopes. In this study, various microstructure and strength tests were performed on SFCTB, considering steel fiber ratio and electromagnetic induction strength effects. Lab findings show that combining steel fibers and their distribution dominantly influences the improvement of the fill’s strength. Fill’s strength rises by fiber insertion and has an evident correlation with fiber insertion and magnetic induction strength. When magnetic induction strength is 3 × 10⁻⁴ T, peak uniaxial compressive stress reaches 5.73 MPa for a fiber ratio of 2.0vol%. The cracks’ expansion mainly started from the specimen’s upper part, which steadily expanded downward by increasing the load until damage occurred. The doping of steel fiber and its directional distribution delayed crack development. When the doping of steel fiber was 2.0vol%, SFCTBs showed excellent ductility characteristics. The energy required for fills to reach destruction increases when steel-fiber insertion and magnetic induction strength increase. This study provides notional references for steel fibers as underground filling additives to enhance the fill’s durability in the course of mining operations.