[Objective] This study aimed to clarify the spatial distribution patterns of soil erosion, soil aggregates, and aggregate-associated organic carbon in the grassland and terraced fields in the agro-pastoral ecotone of Qilian Mountains, and to elucidate how soil erosion drives the redistribution of aggregate-associated organic carbon along slopes. The findings will provide a theoretical basis for soil conservation and carbon sequestration in this region. [Methods] Typical grassland and terraced fields were selected as the study objects. The ¹³⁷Cs tracer method was used to estimate the rates of water erosion and tillage erosion. The wet sieving method was used to separate aggregates into four particle sizes fractions. The mean weight diameter（MWD）, geometric mean diameter（GMD）, organic carbon content in each aggregate size fraction, and organic carbon content were calculated.[Results] 1) The soil ¹³⁷Cs inventory exhibited a "decrease-increase-decrease-increase" trend along the slope direction of the grassland. However, the soil ¹³⁷Cs inventory exhibited a fluctuating increase, with a sharp mutation at the junction of Terrace 1（T1） and Terrace 2（T2）. 2) The total erosion rates ranged from-17.55 to 4 579.69 t/（km²·a） in grassland and-1 358.10 to 11 226.20 t/（km²·a） in terraces. Higher soil erosion rates were found at the top of each terrace than that in the grassland. 3) The aggregate composition varied among different slope positions. In the grassland, large macroaggregates（ ＞2 mm） dominated at all landscape positions, whereas in terraced fields, small macroaggregates（0.25-2 mm） were dominant. The MWD and GMD of grassland aggregates were higher than those of terraces. Along the downslope direction of terraced fields, the mass fraction of ＞2 mm aggregates and aggregate stability showed a fluctuating increase, while the fraction of ＜0.25 mm aggregates exhibited the opposite trend. For both grassland and terraced fields, the aggregate-associated organic carbon showed a fluctuating trend of increase in the downslope direction, but the increase in organic carbon content at the foot position of the terraced fields（191.15% higher than that at the summit） was significantly greater than that in the grassland（25.70% higher than that at the summit）. [Conclusions] In the agro-pastoral ecotone of the Qilian Mountains, the combined effects of tillage erosion and water erosion in sloping croplands exacerbates the fragmentation and migration of ＞2 mm aggregates, reducing aggregate stability at the slope summit, and consequently leading to organic carbon depletion at the summit and accumulation at the foot position of the slope.