【Objective】This study aims to reveale the law of soil quality variation caused by water erosion provides scientific data support for soil erosion control and low-efficiency forest transformation in hilly red soil region of southern china.【Method】The small watershed of Qingyuan Mountain in Ji ’an City, Jiangxi Province was selected as a typical area of red soil hilly area in southern China. According to the typicality and representativeness, the small watershed was divided into slope positions, and three sections were set up to collect soil repeatedly. The composition of soil aggregates was analyzed, and the correlation analysis was used to explore the relationship between various indicators in the process of water erosion.【Result】Water erosion changed the spatial distribution pattern of bulk density and soil porosity, resulting in weaker soil anti-erodibility in erosion area and less influence in deposition area, which accelerated the occurrence of soil erosion. Soil bulk density increased after long-term erosion. Compared with other slope positions, soil bulk density at slope toe increased significantly by 0.16 g/cm³ (P < 0.05), while saturated water holding capacity and capillary porosity decreased significantly (P < 0.05). After water erosion, the composition of soil texture also changed, soil sand content increased significantly, clay and silt content decreased significantly (P < 0.05). The water erosion process had different effects on soil nutrients at different slope positions. The soil total nitrogen, available phosphorus, organic carbon content and carbon-nitrogen ratio decreased on the upper, middle and lower slopes, and the content on the slope decreased significantly (P < 0.05). Compared with other slope positions, the nutrient content at the toe of the slope increased, and the available phosphorus increased significantly by 39.31% (P < 0.05). After water erosion, the mass fraction (R_0.25), mean mass diameter (MWD) and geometric mean diameter (GMD) of water-stable aggregates at different slope positions showed a decreasing trend, and the change at the foot of the slope was not obvious, and the stability of soil structure was the highest.【Conclusion】The ecosystem of red soil hilly area in southern China is fragile. Long-term water erosion can reduce the stability of red soil aggregates. The water erosion process causes spatial differentiation of soil physical and chemical properties in erosion-deposition sites. Vegetation coverage and litter thickness are the main environmental factors.