Abstract: To achieve efficient resource utilization of yellow phosphorus smelting solid waste, a systematic experimental study was conducted on the activation of the latent reactivity of yellow phosphorus slag (YPS) and its application in mine backfill. First, proportioning tests for YPS-based cementitious materials were carried out to investigate the optimal binder formulation that balances reactivity and cost-effectiveness. Based on the optimized binder, backfill tests using all-phosphorus-based solid waste were conducted to explore the effects of binder-to-aggregate ratio, binder substitution rate, and aggregate ratio on the strength evolution of the backfill body. Furthermore, microscopic characterization methods, including Thermogravimetric Analysis, X-ray Diffraction, and Scanning Electron Microscopy, were employed to corroborate the strength evolution laws from the perspectives of hydration products and microstructure.The results indicate that the YPS-based cementitious material achieved a maximum 28-day compressive strength of 13.15 MPa under synergistic activation with 20% CaO, 26.7% fly ash, and 5% Na2SO4. Applying this optimal binder to the phosphogypsum-YPS synergistic backfill system, and considering practical phosphate mining conditions, the optimal backfill parameters were determined as: a binder-to-aggregate ratio of 1:2, an aggregate ratio (PG:YPS) of 3:1, and a binder substitution rate of 33%. The resulting 28-day strength reached 3.45 MPa, meeting mine backfill requirements. The dual alkali-sulfate activation effectively promoted the formation of ettringite and C-S-H gel as well as pore densification, thereby elucidating the strengthening mechanism of the macroscopic mechanical properties.