Owing to severe erosion, ecosystems in the Loess Plateau in China are regarded as the most fragile habitats globally. Therefore, it is fundamental to explore the response of water erosion dynamics to vegetation cover and slope allocation, aiming at the accurate prediction and control of sediment yield. In the present study, the WEPP(Water Erosion Prediction Project) model was used to simulate the rainfall-erosion process at a hillslope scale, and the changing processes of soil erosion under different rainfall intensities (0.5, 1.0, 1.5 mm/min), vegetation canopy cover (20%, 40%, 60%, 80%), and slope position (upper, middle, lower) were analyzed. The responses of sediment yield to the interaction effects of vegetation canopy cover and slope positions were revealed by a double factor variance analysis and relative contribution index. The results showed that an increase of vegetation canopy cover reduced soil loss and sediment yield significantly, and the least soil loss occurred when the vegetation was distributed in the lower slope conditions. At a low (0.5 mm/min) rainfall intensity, with increased vegetation canopy cover, the interception rate of sediment of Caragana and Stipa bungeana increased from 38% to 90% and 64% to 96%, respectively. At medium (1.0 mm/min) and high rainfall (1.5 mm/min) intensities, when the vegetation canopy cover was < 20% or > 80%, the sediment yield of the S. bungeana slope was greater than that of the Caragana slope. However, when the vegetation canopy cover was between 40% to 60%, the sediment yield of the S. bungeana slope was less than that of the Caragana slope. Meanwhile, a double factor variance analysis showed that slope position and vegetation cover exhibited a significant effect on sediment yield on slopes (P < 0.001). Specifically, the interaction between the slope position and S. bungeana vegetation cover showed a significant effect on sediment yield (P < 0.01), but when the vegetation changed to Caragana, the interaction between slope position and vegetation cover became insignificant on sediment yield. Moreover, when S. bungeana was allocated on the down slope, or when the allocation of Caragana and S. bungeana was 1:2, both captured the least sediment yield.