Abstract: Background The soil structure on coal mine waste dump slopes is loose with poor water and nutrient retention capacity, making vegetation cover critical to soil erosion control. This study investigates the synergistic effects of vegetation cover and soil improvement measures on controlling soil erosion on slopes of open-pit coal mines in cold-region grasslands, while evaluating the soil conservation effectiveness of existing soil improvement practices in mining areas. Methods This study employed artificial rainfall simulation tests to analysis the combined effects of varying vegetation cover levels (0%, 30%, 60%, and 90%) of Leymus chinensis (Trin.) Tzvel. + Medicago sativa L. and soil improvement measures (2% expanded clay aggregate, 0.4% microbial inoculant, and 5% weathered coal uniformly mixed or sprayed onto native topsoil) on runoff and sediment yield patterns at slopes subjected to rainfall intensities of 30 mm/h, 40 mm/h, 50 mm/h, and 60 mm/h. Results 1) Runoff generation rates on waste rock dump slopes exhibited a “initial increase followed by stabilization” pattern with rainfall duration. Vegetation coverage significantly reduced runoff generation rates, with 90% coverage yielding only 1/5 to 1/3 of bare slope runoff; Soil improvement effectively suppressed runoff generation. Under moderate to high rainfall intensities (≥40 mm/h), the total runoff volume on improved slopes with 90% coverage decreased by 24.4%–27.6% compared to unimproved slopes, with both factors synergistically mitigating rainfall intensity effects. 2) Sediment yield exhibited three distinct phases: rapid initial increase, rapid mid-phase decrease, and stable late phase. Cumulative sediment yield significantly decreased with increasing vegetation coverage. At 30 mm/h rainfall intensity, sand yield on unimproved slopes with 90% coverage was only 4.3% of bare land levels, increasing with rainfall intensity. Soil improvement enhances erosion resistance, reducing slope sand yield by 28.7% at 60% coverage + 40 mm/h rainfall intensity, forming a synergistic sand retention effect with vegetation. 3) Cumulative sediment yield exhibited a significant positive linear correlation with runoff volume (R²≥0.9021). Sixty percent vegetation cover served as the threshold for weakening water-sediment coupling intensity. Higher cover reduced incremental sediment yield by over 70% under identical runoff conditions, while soil improvement further moderated the water-sediment response relationship. (4) Vegetation regulates sediment through canopy interception and root retention, while soil improvement enhances infiltration capacity by optimizing structure. Their synergistic effect outperforms individual measures. Conclusions This study clarifies the runoff-sediment coupling patterns in grassland mining waste dumps. The “vegetation + soil improvement” synergistic control system achieves research objectives, providing technical parameters for precise soil erosion prediction and ecological restoration.