[Objective] The characteristics and processes of soil nutrient loss in the platform slope system of a discharge site in China’s mining area were analyzed in order to provide a theoretical basis for preventing and controlling nutrient loss at discharge sites. [Methods] Using the discharge site of the Haizhou open-pit coal mine in Fuxin City, Liaoning Province, as the research object, an indoor model of the platform-slope system of the discharge site was established through the principle of a similar simulation, and an artificial rainfall simulation test was used to study the process and characteristics of nutrient loss from the platform-slope system of the discharge site under different rainfall intensities (60, 90, and 120 mm/h). [Results] ① With escalating rainfall intensity, the soil nutrient concentrations for nitrogen, phosphorus, and potassium in the dump waste platform-slope system exhibited a pattern of initial decline, subsequent rise, and then a gradual decrease, 60 mm/h ＞ 90 mm/h ＞ 120 mm/h for each intensity. ② The runoff nutrient loss from the platform slope soil increased with increasing rainfall intensity, notably for total nitrogen (TN), total phosphorus (TP), and total potassium (TK). However, the loss of nitrate (NO^-₃-N), ammonium (NH⁺₄-N), available phosphorus (AP), and available potassium (AK) in runoff did not change significantly with increasing rainfall intensity. ③ The nutrient concentration in the soil sediment from the dump waste platform slope consistently exceeded that found in surface runoff, with sediment nutrient loss escalating as the rainfall intensity increased. ④ The enrichment ratio of total nitrogen and total potassium in soil sediment rose with greater rainfall intensity, expressed as TN ＞ TP＞ TK. [Conclusion] The concentration of soil nutrients lost in the dump waste platform-slope system was predominantly influenced by rainfall intensity and soil characteristics.