This paper overlayed the coverage of land-resource-type map with single-factor-coverages of each evaluation factor separately. The spots on land-resource-type map were studied as evaluation units for soil quality,attributes were extracted from the polygon attribute table (PAT) of each resulted coverage, such as elevation, slope, soil organic material content, soil texture,soil pH, land uses, landform type and soil type. Decision tree is used to predict soil quality grade, the knowledge are expressed in quantitative rules. The results showed that it was easy to understand the knowledge,and accuracy could be 96.61%.