Abstract: Aiming at the environmental pollution problems caused by large-scale storage of phospho⁃ gypsum and the hidden dangers of geological disasters in mine goaf，based on the engineering practice of Qingping Phosphate Mine，the optimization of underground filling ratio and field industrial test of modified dihydrate phosphogypsum were carried out. Phosphogypsum was used as the main material，and fly ash， lime and special admixtures were compounded to optimize the filling ratio. The engineering applicability and environmental safety of the filling technology were systematically verified by mechanical property test，toxic⁃ ity leaching test，retaining wall mechanical checking and whole process monitoring of global water environ⁃ ment. The test results show that the modified phosphogypsum filling body with optimized ratio has excellent working performance and can realize underground gravity transportation. The 28 d compressive strength reaches 6.19 MPa，which meets the design requirements of mine filling support. The modified system can ef⁃ fectively solidify harmful ions such as phosphorus and fluorine. The leaching concentrations of fluoride and phosphate in the filling body are 0.604 mg/L and 0.04 mg/L，respectively，which meet the standard of Class I general industrial solid waste and have good environmental compatibility. Field industrial test and water quality monitoring confirmed that the layered filling construction technology was safe and reliable，and the filling operation did not cause adverse effects on the regional groundwater and surface water environment.The economic benefit analysis shows that compared with the traditional sand-gravel filling process，this technology can save the filling cost by 25.494 million yuan/a. It can absorb the solid waste of phosphogyp⁃ sum on a large scale，control the underground goaf，and realize the synergistic benefit of waste treatment and green mining. It can provide reliable engineering reference and technical demonstration for the resource utilization of solid waste in phosphate mines and the treatment of goaf.

Key words: phosphorus mine, goaf filling, modified dihydrate phosphogypsum, industrial test, water quality monitoring