Abstract: Background This study aims to conduct an in depth analysis of the spatiotemporal distribution patterns of runoff and sediment and their response to vegetation-slope coupling in the Hantaichuan watershed, and to provide a scientific basis for precise soil erosion control in the Ten Tributaries area. Methods The Mann Kendall trend test and linear fitting were used to analyze the interannual variations and the relationship between runoff and sediment. The GeoWEPP model was employed to identify key source areas of erosion and sediment yield as well as transport pathways. A spatial overlay analysis of soil erosion intensity, vegetation coverage, and slope gradient was conducted to examine the individual and coupled effects of vegetation and slope on the erosion pattern. Results (1) From 2006 to 2020, neither runoff nor sediment load showed a significant trend in the Hantaichuan watershed, and the runoff–sediment relationship was generally stable. Runoff and sediment load exhibited a significant positive correlation, and sediment transport was highly sensitive to runoff changes. (2) Soil erosion in the watershed was dominated by slight and light erosion. The areas near the main channel banks and tributary confluences in the middle and lower reaches were key source areas of sediment export; the middle and lower main channel served as the core pathway for runoff and sediment transport. (3) Vegetation coverage and soil erosion intensity generally showed a negative correlation, with 30% vegetation coverage being a potential threshold. Slope gradient exhibited a distinct threshold effect on erosion intensity, with the 24°–30° slope range being the critical gradient zone for moderate to high intensity erosion. Areas with a slope of 18°–36° and vegetation coverage below 25% were identified as key zones for soil and water conservation efforts. Conclusions The critical source areas of runoff and sediment generation in the Hantaichuan watershed were concentrated near the river channels in the middle and lower reaches, and both vegetation coverage and slope gradient jointly regulated the watershed erosion pattern.