As the most easily eroded land-use type, severe soil degradation of the plow layer (as a shallow soil layer), deterioration of soil properties, and gravel process, could restrict the sustainable utilization of slope farmland, which also directly threatens local food security and ecological security. Plow-layer soil quality is highly sensitive to both natural factors and artificial farming tillage. Taking the plow-layer soil quality of three slope farmlands in the southern purple hilly area (Hechuan-Chongqing, Xingguo-jiangxi, and Chuxiong-Yunnan) as examples, this study mainly analyzed the differences in soil physical properties, soil reservoir characteristics, and soil nutrient characteristics of slope farmlands, and their vertical distribution characteristics, from the perspective of soil properties, so did the forming causes at the same time. The results indicated the following. (1) The soil organic matter of the plow-layer in the three locations in decreasing order was as follows: Chuxiong-Yunnan (28.80 g/kg) > Xingguo-jiangxi (9.03 g/kg) > Hechuan-Chongqing (8.80 g/kg). With the exception of total soil potassium content, other contents such as total soil nutrients and available soil nutrients, could be arranged in the following order: Chuxiong-Yunnan > Hechuan-Chongqing > Xingguo-jiangxi. The vertical characteristics of available soil nutrients in the plow-layer of slope farmland showed the same distribution, being mainly concentrated in the 0-20-cm soil layer. However, there were no significant differences between the 20-40-cm soil layer and the 40-60-cm soil layer. (2) The soil physical properties of the plow-layer of slope farmlands among the three purple hilly locations showed significant differences. The soil physical quality of the plow-layer in Hechuan-Chongqing was the worst, with the characteristic of soil sand content > 60%, maximum soil bulk density of 1.43 g/cm³, minimum soil total porosity of 45.97%, and capillary porosity of 34.36%. From the viewpoint of the plow-layer vertical characteristics of slope farmland, the soil physical properties of the tillage layer (0-20 cm) were better than those of the subsoil (20-40 cm) and bottom layer (40-60 cm). (3) The initial soil infiltration rate of the plow-layer in the Xingguo-jiangxi slope farmland was the largest (0.32 mm/min), and the initial soil infiltration rate in Hechuan-Chongqing plow-layer was the lowest (0.19 mm/min). The soil infiltration rate and the average soil infiltration rate both showed the same order of Chuxiong-Yunnan > Xingguo-jiangxi > Hechuan-Chongqing. The soil maximum effective capacity of the plow-layer in Chuxiong-Yunnan slope farmland was the best (873.311 t/hm²), which indicated that such plow-layers of slope farmland have better resistance to seasonal drought. Plow-layer vertical characteristics, such as the total storage capacity, dead storage capacity, active storage capacity, flood detention storage capacity, and maximum effective capacity, all showed the same order: tillage layer (0-20 cm) > subsoil layer (20-40 cm) > bottom layer (40-60 cm). (4) The soil shear strength and the soil penetration resistance of the plow-layer among the three slope farmland locations showed the same regular changes. The soil shear strengths of the plow-layer were Hechuan-Chongqing (15.39 kg/cm²) > Chuxiong-Yunnan (14.74 kg/cm²) > Xingguo-jiangxi (10.66 kg/cm²), whereas the soil penetration resistances of the plow-layer were Hechuan-Chongqing (424.83 kPa) > Chuxiong-Yunnan (252.50 kPa) > Xingguo-jiangxi (188.87 kPa), which indicated that the plow-layer soil of slope farmland in the Hechuan-Chongqing purple hilly area has better resistance to shear stress and greater resistance to farming tillage. These results could provide a theoretical basis and supporting data not only for soil quality diagnosis but also for rational plow-layer evaluation for slope farmlands in different purple hilly areas.