Different patterns of soil erosion cause differences in soil aggregate breakdown and its loss processes. Previous studies concentrated mainly on the variation in soil aggregates under various land uses and breakdown mechanisms. This paper used simulated rainfall experiments to investigate how sheet and gully erosion affected soil aggregate losses. The tested soil is black soil collected from Yushu city in Jilin Province and the experiment was conducted in the simulated rainfall hall of the Institute of Soil and Water Conservation. The lateral spraying nozzles, whose height was 16 m above the ground, were used in this study. The size of the test soil pan was 8 m long, 3 m wide and 0.6 m deep. The experimental design covered two rainfall intensities of 50 and 100 mm/h, one slope of 10°, and two erosion patterns of sheet and gully, and each treatment had two replications. During the rainfall process, runoff samples were collected and lost aggregates were collected through a set of sieves with different apertures of 5, 2, 1, 0.5 and 0.25 mm in every five minutes. The dry sediment was used to calculate erosion rate and different sizes of dry lost aggregates in the sediments were used to compute aggregate loss. The results showed that under rainfall intensities of 50 and 100 mm/h, the gully erosion rate was almost 1.42 and 3.51 times greater than that of sheet erosion, respectively. When the rainfall intensity increased from 50 to 100 mm/h, the < 0.25 mm micro-aggregates in the sediments from sheet erosion treatment increased from 45% to 74%; while for the gully erosion dominated treatment, the aggregate in the sediments was mainly comprised of ≥0.25 mm of macro-aggregates, which occupied 65.5% of total aggregate loss. Under the rainfall intensity of 50 mm/h, > 5 and 2-5 mm aggregates in the sediments from the sheet erosion treatment were lower than those from the gully erosion dominated treatment; while the other sizes of aggregates in the sediments from the sheet erosion treatment were greater than those from the gully erosion dominated treatment. Under 100 mm/h of rainfall intensity, all sizes of aggregates in the sediments from the gully erosion dominated treatments were greater than those from the sheet erosion treatment. The results also demonstrated that, for the sheet erosion treatment, raindrop impact was the main driving force for aggregate breakdown, while for the gully erosion dominated treatment, concentrated flow detachment, transportation in gully channel and friction function of the different aggregates during transportation processes were the main driving forces for aggregate breakdown. Compared with the test soil, mean weight diameter (MWD) and geometric mean diameter (GMD) of aggregates in the sediments were lower for both treatments of sheet and gully erosion. Under the two rainfall intensities of 50 and 100 mm/h, MWD and GMD in sediments from the sheet erosion treatment were smaller than those from the gully erosion dominated treatment. This paper also proposed that under the experimental conditions, two indicators of MWD and GMD could reflect the lost aggregate characteristics, and MWD could better reflect aggregate variation with an increase in rainfall intensity.