Abstract: Under the condition of secondary rainfall, straw mulching may affect the sorting effect of runoff on sediment and thus change the aggregate distribution of eroded sediment. In order to clarify the influence of straw mulching on the aggregate distribution of eroded sediment on purple slope cultivated land, different straw mulching amounts (0, 0.2, 0.4, 0.6, 0.8 kg/m²) and gradients (10°,15°,20°) were adopted. Under the indoor artificial rainfall conditions, the change characteristics of the content of each particle size (<0.002, 0.002-0.05, 0.05-2 mm) and its enrichment rate (ER) and median particle size (D_0.5) in the eroded sediment were investigated. The results show as follows: 1) The variation trend of <0.002 mm eroded sediment aggregates with rainfall duration is stable, and the variation trend of 0.002-0.05 mm and 0.05-2 mm eroded sediment aggregates with rainfall duration is gradually decreasing and increasing, respectively. 2) With the increase of straw cover amount, the aggregate content of <0.002 mm increased first and then decreased, and the aggregate content of 0.002-0.05 mm increased as a whole. Compared with the bare slope, 0.8 kg/m² straw mulching can significantly reduce the <0.002 mm aggregate content by 30.97-55.46%, indicating that the purple slope under straw mulching mainly lost <0.002 mm aggregate content. Under straw covering on a 15°, the aggregate content of 0.002-0.05 mm at 0.2 kg/m² was significantly lower by 22.54%, 21.09%, 36.01% and 19.29% than that of 0, 0.4, 0.6 and 0.8 kg/m². At 10° slope surface, the 0.05-2 mm eroded sediment content of 0.2 kg/m² straw mulch was significantly higher than that of the other 4 straw mulch covers. 3) Under the same slope, the median particle size initially increased and then decreased with the increase of straw cover amount, and the change of median particle size with the slope was affected by the straw cover amount. The median particle size content of 0.8 kg/m² on 20° slope was significantly higher by 26.28%, 37.03% and 34.48% than that of 0, 0.4, and 0.6 kg/m². 4) Under the conditions of slope and straw cover, ER_0.002-0.05 is greater than 1, while ER_<0.002 and ER_0.05-2 are less than 1. ER_<0.002 had no difference at 10° and 20° under the coverage of 0 kg/m² and 0.4 kg/m², and the other conditions had significant differences. Under the three gradients, the ER_0.002-0.05 of 0.2 kg/m² mulch was significantly lower than that of the other four covers, and showed a trend of first decreasing and then increasing with the increase of straw mulch. The ER_0.05-2 of 0.2 kg/m² coverage at each slope was significantly higher than that of other coverage (P<0.05). When the coverage of straw was 0 kg/m² and 0.6 kg/m², the ER_0.002-0.05 on the 15° slope was significantly higher than that on the 10° and 20° slopes. 5) There is a significant quadratic function relationship between the aggregate content and enrichment rate of <0.002 mm and the straw mulch amount, and the major maximum is reached when the straw mulch amount is 0.2 kg/m². When the amount of straw applied is greater than 0.4 kg/m², the loss of clay particles can be effectively reduced.The results of this study will deepen the understanding of the distribution law of eroded sediment in slope farmland in purple soil area, and provide scientific basis for the optimization of straw mulching measures.