Quantitative evaluations of the cultivated-layer quality (CLQ)of sloping farmland are important for the effectively improving and rationally utilizing of the cultivated layers. Using a red soil watershed as the research object, we quantitatively analysed the relationship among factors influencing the CLQ using structural equation modeling based on the DPSIR framework (A framework for describing the interactions between society and environment developed by the European Environmental Agency) to describe the CLQ evolution process. We identified the key indicators of the driving factors (D) during cultivated-layer degradation and critical environmental pressure (P) to construct a reasonable cultivatedlayer (RCL) by principal component analysis (PCA). We defined the main CLQ diagnostic indicator set to assess the CLQ by factor analysis and analysed the reasonable measures to improve the CLQ. The results show quantified direct or reverse effects among D, P, state performance (S), problem impacts (I) and response strategy (R). The contribution rates of D and P were affected by the comprehensive effects of natural and human factors or human factors along. The CLQ diagnostic indicator set included 7 soil indicators and sub-soiling is the main adjusted measure for cultivated-layer recovery. These results could provide important technological paths for objectively understanding the causes drivers of the degradation and improving the CLQ for red soil sloping farmland.