To address the issues of short setting time, poor water resistance and inadequate strength when β-hemihydrate phosphogypsum (β-HPG) is used as backfill cementing materials, two industrial solid wastes, carbide slag and silica fume were introduced. The effects of these wastes on the workability, water resistance, and strength of β-HPG were analyzed. The microstructure and pore structure of the modified β-HPG were investigated by SEM. Additionally, the environmental behavior, cost, and carbon emissions of the modified β-HPG were evaluated. The results indicate that the combined use of carbide slag and silica fume significantly extends the setting time of β-HPG slurry and enhances its fluidity. After modification, the compressive strength of β-HPG backfill is substantially increased, reaching a 28-day strength value of 36.6 MPa, with a reduced water absorption rate of 2.7% and an elevated softening coefficient of 0.885. The incorporation of silica fume and carbide slag can improve the micromorphology and pore structure of β-HPG backfill. The generated calcium silicate hydrate, a hydraulic hydration product, enhances the compactness of backfill. Carbide slag and silica fume effectively neutralize residual acids in the β-HPG and immobilize phosphorus and heavy metal elements within the hardened body. When the content of carbide slag is 10% and the content of silica fume is 15%−20%, the β-HPG cementing material exhibits favorable economic and environmental benefits.