Soil erosion is a serious problem that has significant environmental impacts, including declines in soil quality, sedimentation of reservoirs, and nonpoint source water pollution. Thus, it is important to study soil erodibility and mechanisms for nutrient loss on sloping land. Plenty of studies have researched soil erosion factors, such as land use patterns, plant cover type and ratio, slope length and gradient, rainfall intensity and amount, and raindrop kinetic energy; these studies have been key to characterizing these processes. It is generally recognized that plant cover and slope length have a significant impact on soil erosion and nutrient loss. However, these parameters have often been studied in isolation, and few have researched the combined effects of sedimentation and nutrient loss. In this study, we analyzed the effects of slope length and plant cover ratio on the particle size distributions (PSDs) of soil and eroded sediments from sloping vegetated fields under heavy rainfall. We evaluated the change in soil aggregate stability characteristics to explain the relationship between PSDs of the eroded sediment and soil aggregate stability. Twelve simulated rainfall experiments were conducted in a glasshouse with a rainfall intensity of 2mm/min and runoff was produced within 30min. For this study, we implemented three slope lengths, 2, 3, and 4m, and four levels of vegetation cover ratios, 0, 30%, 60%, and 90%, in 2014 and 2015. The micropipette method was used for particle size analysis of soils and eroded sediments. Surface soil samples before and after rainfall were separated into five soil aggregate sizes, > 2mm, 1-2 mm, 0.5-1mm, 0.25-0.5mm, and < 0.25mm, by dry sieving and wet sieving. The experimental indexes to evaluate soil aggregate stability included water stable aggregates (WSA), mean weight diameter (MWD), and dispersion degree of soil aggregate (PAD). The results showed that clay particles ( < 2μm) and fine silt particles (2-20μm) were the main size fractions in eroded sediments. Surface runoff, which causes soil erosion, is a selective transport process; hence, there were more clay particles and fine silt particles in the eroded sediments (approximately 57.08%) than in the original soils (43.92%). The proportion of clay particles in the eroded sediment increased slightly as the vegetation cover ratio increased. There were no significant differences in PSDs of eroded sediments for different slope lengths with the same cover ratio (P > 0.05). The content of > 2mm and > 0.25mm PAD (PAD_0.25, PAD₂) increased, whereas the content of > 0.25mm WSA (WSA_0.25) decreased after rainfall. Vegetation cover ratio had a more significant effect on > 0.25mm soil aggregate stability than did slope length. We found that the WSA index generally reflected the difference in soil structure stability. WSA_0.25 was the main factor affecting PSDs of eroded sediments; the MWD content of the eroded sediments decreased gradually whereas WSA_0.25 content increased. We also found a significant negative correlation between PSDs of eroded sediment and MWD of soil aggregate. Finally, we observed that more stable soil macro-aggregates resulted in less coarse soil surfaces.