In this study, the purple soils under different typical vegetation cover conditions (Quercus franchetii Skan, tree; Osteomeles schwerinae C.K.Schneid, shrub; Eleusine indicate (L.) Gaerth, grass) were selected in the dry-hot valley area of Yuanmou of Yunnan Province in order to investigate the effects of root morphological characteristics in different soil layers on soil nutrient contents and chemical alteration index (CAI). The results showed that soil CAI was ranged from 73.98–78.87 for bare soil (CK), 78.53-84.68 under trees, 77.89–82.18 under shrubs and 77.91–81.04 under grasses, respectively, and all were decreased with the increase of soil depth. The roots of all kinds of plants were concentrated within the 0–20 cm soil layer, and plant type significantly affected root volume, compared to CK, root volume was enhanced by 145.17% under trees, 144.78% under grasses and 74.98% under shrubs, respectively; and root surface area was increased by 651.16% under trees, 610.79% under shrubs and 181.62% under grasses, respectively. Soil nutrient contents were generally decreased with the increase of soil depth, particularly for the contents of organic matter (SOM), alkali-hydrolyzale (AN), available phosphorus (AP) and available potassium (AK), soil pH showed an increasing trend in CK and under trees, but showed a decreasing trend under grasses and shrubs. The results of correlation analysis showed that soil CAI value was significantly positively correlated with SOM and AN content, with correlation coefficients as high as 0.520 and 0.591 (P<0.05); soil pH and AP content were significantly negatively correlated with soil CAI value (P<0.05), and soil CAI value was highly significantly positively correlated with root volume and root surface area, with correlation coefficients as high as 0.693 and 0.621 (P<0.01). respectively. In conclusion, plant root distribution has a more significant contribution to the chemical weathering of purple soils.