Scientific determination of index areas and participating factors is the premise and foundation for accurate farmland gradation.On the basis of the analysis of the purposes,principles and requirements of the determination of index areas and participating factors for farmland gradation,Yixing County of Jiangsu Province was cited as a case study.Division of index areas for farmland gradation and determination of the principal gradation participating factors for every index area were attempted by the cluster analysis method and the principal component analysis method.The results indicated that with the quantitative analysis method,gradation index areas could be divided and their gradation principal part icipating factors determined objectively and scientifically,which made the final gradation more accurate.