Abstract: Studies of sediment particle distribution and sorting properties at different gradations can reveal hillslope soil erosion mechanisms and better understand the processes of sediment detachment, transport, and deposition on purple soil slopes. In this study, the research object selected was the typical purple soil in southwest China. The indoor water flushing experiments were carried out on the purple soil slopes, with two types of slope gradients: 10° and 15°, and three types of flow discharge conditions: 4, 6, and 8 L/min. The rill erosion processes as well as the various characteristics of sediment particles on the slope were thoroughly investigated.?The results showed that: 1) the runoff rate and sediment yield rate of 10° and 15° slopes both increased with the increase of flow discharge conditions. Under 6 L/min and 8 L/min flow discharge conditions, the average runoff rate of each slope increased by 1.35-2.37 and 1.70-1.97 times, respectively, compared to the flow discharge condition of 4 L/min. The average sediment yield rate increased by 1.31-3.51 and 7.70-8.58 times. As a whole, the influence of slope gradient on sediment yield rate was greater than that of runoff rate. 2) The silt was the main particle composition of the eroded sediment on each slope, ranging from 47% to 55% depending on the flow discharge conditions. The Enrichment Ratio (ER) and Aggregation Ratio (AR) of eroded sediment particles with different grain sizes differed significantly. The ER of clay particles was less than 1, and the AR was more significant than 1, which indicated that the sediment particles of this size were quickly lost in the process of erosion and migrated in the form of aggregates. Furthermore, the ER of silt particles was more significant than 1, indicating that particles of this size were enriched in the eroded sediment. The AR of silt particles was close to 1, which stated that the majority of them migrated as primary particles. For different slopes, the enrichment ratios of clay and silt in eroded sediment increased with the increase in flow discharge conditions, indicating that the rise in discharge would affect the enrichment of fine particles. Under the conditions of high flow discharge, fine particles were more susceptible to enrichment.?3) The volume fractal dimension varied from 2.43 to 2.63 in different flow discharge conditions and showed a decreasing trend with the duration of the scouring time. Furthermore, the volume fractal dimension had a very significant positive correlation with clay and silt content and a very significant negative correlation with sand content. The volume fractal dimension values were primarily determined by the clay particle content. The research can help to clarify the laws of the sediment particle size varying with the development of the rill erosion process on a slope. Meanwhile, it can provide data support and a theoretical basis for particle size selection of fingerprint factor and reveal the erosion mechanism on a slope.