Over the past 30 years, vegetation restoration on the Loess Plateau, China, has yielded remarkable results. However, the impact of different vegetation restoration stages on slope erosion control and sediment source-sink dynamics during succession remains unclear. Consequently, in-situ scouring experiments were conducted in Loess hilly and gully Ito assess vegetation restoration stages on runoff and sediment and to understand erosion-deposition transitions. Treatments comprised three inflow rates (4, 8, and 16 L/min), four vegetation succession stages (1, 11, 15, and 25 years), and three consecutive scouring periods (0-30, 31-60, and 61-90 min), with 3D laser scanning used for topographic analysis. Results showed that the capacity of vegetation to slow runoff and reduce erosion did not increase linearly with succession duration. The 11-and 25-year succession stages achieved the greatest reductions in runoff and sediment. At year 25, heavily deposited areas (<-10 mm) increased by 480.17 % in size and 33.13 % in depth compared to early succession. The primary erosion evolution path was mild deposition > mild erosion > moderate erosion, with high scouring flow rates accelerating this dynamic process. With natural succession, sediment source-sink transitions on slopes gradually stabilized, and non-converted areas during erosion were 71.62 % (year 1), 61.18 % (year 11), 68.26 % (year 15), and 53.00 % (year 25). Over time, the slopes transitioned from an erosion-dominated state to more stable conditions. This study offers a more systematic evaluation of the dynamic outcomes of the Grain for Green Project, supporting soil conservation and ecological restoration of the Loess Plateau.