Abstract: To investigate the characteristics of soil quality changes during the development of steep-slope tea gardens, a large-scale tea garden in Shangnan County, Shaanxi Province, was selected as the study area. A systematic analysis was conducted to examine the effects of different slopes (10-40°) and planting durations (1-20 years) on soil erodibility and nutrient evolution in tea gardens. The results showed that: (1) The levels of ammonium nitrogen, available phosphorus, total nitrogen, and organic matter in tea garden soils decreased with increasing slope angle. Compared with the control group, the total nitrogen and organic matter in tea garden soils at a 40° slope angle decreased significantly by 41.13% and 66.67%, respectively. nitrate nitrogen decreased significantly by 70.59% (P < 0.05) at slopes greater than 20°, and the sand particle content reached its highest level at a 40° slope, while clay and silt content decreased, resulting in soil erodibility being 31.17% lower than the control group (0° tea garden). (2) In the 40° steep slope tea garden, newly cultivated tea gardens experienced soil erosion due to topsoil disturbance and vigorous nutrient absorption by tea plants, resulting in a decrease in organic matter content and a significant increase in soil erosion potential (P < 0.05) over five years. As planting duration increased (10-20 years), vegetation cover improved, root activity and litter input promoted a 28.31% increase in organic matter content, nitrogen cycling rates increased, and soil erosion resistance strengthened. (3) Soil erodibility showed a significant positive correlation with silt and clay particles (P < 0.05), with correlation coefficients of 0.94 and 0.84, respectively. It also showed a significant negative correlation with sand particles (P < 0.05), with a correlation coefficient of 0.94. This indicates that the loss of fine particles exacerbates nutrient imbalance and structural degradation, while coarse particles, though inhibiting erosion, they are formed due to the loss of fine particles and weaken water and nutrient retention capacity. (4) Soil quality in steep-slope tea gardens exhibits a phased characteristic of “initial degradation followed by later recovery,” with initial degradation being particularly pronounced in newly cultivated tea gardens with a slope of 40°. It is recommended that during the initial cultivation period, measures such as vegetation coverage, drainage measures, and application of organic fertilizers be implemented to mitigate the risks of soil erosion and nutrient imbalance. This study provides a basis for the sustainable management of steep-slope tea gardens and the coordinated regulation of water and soil resources.