Evaluating soil quality in Karst mountains is important to vegetation restoration and desertification control in the rocky region. Based on the analyses of soil fertility characteristics, canonical correspondence analysis (CCA) was used in conjunction with factor analysis to quantitatively assess the soil fertility of scrub, shrub, Lysidice rhodostegia forest, and Excentrodendron hsienmu forest in the Karst mountains of Pingguo County, southwest Guangxi. The results indicated that along with the restoration of vegetation, soil bulk density decreased while soil porosity and soil waterholding capacity increased. Of the four communities, the scrublands had the highest soil pH. Soil organic matter, total nitrogen, and available nitrogen concentrations in L. rhodostegia and E. hsienmu forests were significantly higher than in the scrublands and shrublands. However, soil total phosphorus, total potassium, and available potassium concentrations in the scrublands and shrublands were significantly higher than in the two forests. Soil available phosphorus and exchangeable calcium concentrations showed no detectible differences among the four plant communities. Our results suggested that CCA was effective for screening the soil fertility assessment index, and the integrated assessment scores of soil quality of the four communities were in the order of: L. rhodostegia forest (0.41) > E. hsienmu forest (0.27) > scrub (-0.20) > shrub (-0.44). Lower plant productivity and nutrient accumulation were the primary factors resulting in poor soil quality in the scrublands and shrublands.