Soil aggregates are the basic unit of soil structure and the particle size distribution of surface aggregates play an important role in soil structure and erosion process development.【Objective】 Therefore, the purpose of this study was to explores the mutual transformation of soil aggregates of different particle sizes and the sediment migration path during the interrill erosion and quantify the source characteristics of eroded sediment.【Method】 In this study, a quaternary red clay was collected from Xian’ning in Hubei Province of China, and the soil aggregates were labeled by the rare earth tracer method. Under the condition of 90 mm·h^-1 rainfall intensity, the laboratory simulated rainfall experiment was conducted based on a miniature soil trough with the slope set at 10°. Sediment samples were collected at an interval of 6 min after steady flow production during rainfall, and the contents of rare earth elements in the samples were determined by ICP-MS. A quantitative characterization was also performed on the transformation of soil aggregates within different particle sizes (5~2 mm, large macroaggregates; 2~0.25 mm, small macroaggregates; 0.25~0.053 mm, microaggregates; and <0.053 mm, silt and clay fractions) and the source characteristics of erosion sediment under the Rare Earth Element (REE) concentration.【Result】 The results show that the eroded sediment particles were mainly formed by the same size aggregates transported by runoff, and the content of the sediment particles with the increase of rainfall time. The residual aggregates showed an obvious turnover process and the aggregates with size < 0.25 mm were more easily adsorbed to the aggregates with large size, while the aggregates with size >0.25 mm tended to be broken (the fragmentation rate reached 45.8% and 43.3%), and the broken degree of soil aggregates increased continuously. The characteristics of sediment yield were closely related to the change in topsoil structure and sediment migration and the sediment content of < 0.053 mm and 2~0.25 mm and the contribution rate of the corresponding aggregates in sediment played an important role in the fractal dimension of runoff coefficient and sediment particle size.For the characteristics of erosion sediment production, the sediment content of < 0.053 m and 2~0.25 mm and the contribution rate of the corresponding aggregates in the sediment played an important role in the runoff coefficient and the fractal dimension of sediment particle size.【Conclusion】 Thus, the change of soil topsoil structure and the characteristics of sediment loss during interrill erosion are closely related to aggregate particle size. This further deepens the dynamic process of the interrill erosion and provides a theoretical basis for the soil erosion model and soil and water conservation measures.