Abstract: The leaching of heavy metals and other pollutants in the backfill body is a major potential risk in the backfilling operation of open pits. Based on the backfill slurry filtration test, backfill body immersion test, and solid waste toxicity characteristic leaching procedure （TCLP）, the pollutant leaching risk of the backfill slurry with Dongguashan Copper Mine unclassed tailings and phosphogypsum as backfill aggregate at different time scales was systematically evaluated. The results show that in the early stage of filling, due to the seepage of backfill slurry filtration water, pollutants such as COD, S²⁻, F⁻, TP, and NH₃−N may bring temporary pollution risk to the groundwater of open pits. As the hydration progresses, in the middle stage of filling, all indexes except fluoride can meet the class Ⅲ discharge standard of groundwater, and the growth of hydration products greatly inhibits the leaching of pollutants. Under the long-term occurrence of the backfill body, the heavy metal leaching indexes meet the class Ⅲ quality standard of groundwater.