Abstract: To promote the resource utilization of industrial solid wastes, this study utilized a composite activator consisting of water glass and NaOH, with limestone powder (LP), ground granulated blast furnace slag (GGBS), and fly ash (FA) as cementitious materials, and coal gangue (CG) as aggregate, to prepare a novel backfill material termed ABC. The effects of different water glass modulus, polypropylene fiber (PP) content, and modified waste tire rubber particle (GTR) replacement rate on the workability, unconfined compressive strength (UCS), peak strain, and damage characteristics of ABC were investigated, and the optimal mixing proportions (A3B₂C₂) were determined. Furthermore, the appearance changes, mass loss rate, and UCS loss rate of A₃B₂C₂ and A₃B₀C₀ under dry-wet cycles with sulfate attack were explored, along with micro-characterization of ABC using X-ray diffraction (XRD), thermogravimetric analysis (TG), mercury intrusion porosimetry (MIP), and scanning electron microscopy (SEM). The results indicate that: (1) The A₃B₂C₂ material exhibited the highest UCS (7.12 MPa), while the highest peak strain was observed in the A₃B₂C₄ (1.92 mm). (2) PP provided horizontal tensile stress within the matrix, while GTR transferred and dispersed vertical loads, and the combined use of both increased the number of secondary cracks in the backfill, transitioning the failure mode from tensile to tensile-shear failure. (3) After 90 days of erosion cycles, both A₃B₂C₂ and A₃B₀C₀ maintained their basic shapes with a significant number of aggregates exposed; the mass loss rates were 8.84% and 6.29% for A₃B₂C₂ and A₃B₀C₀, respectively, and the UCS decreased by 43.65% and 35.57%, respectively. The joint use of PP and GTR significantly enhanced the erosion resistance of the backfill. (4) The erosion products included calcium sulfate hexahydrate (Ca₆Al₂(SO₄)₃(OH)₁₂·26H₂O) and gypsum (CaSO₄·2H₂O). After sulfate attack, the toughening and crack resistance effect of PP and GTR on the matrix decreased, but their advantage in resisting degradation remained significantly greater than that of the control group. This research provides a theoretical basis for the practical application of fiber-rubber modified waste-based backfill materials in engineering projects.