The Karamay Agricultural Developing Area is characterized by the advanced farming technology, big investment and complete
infrastructure. However, there are also some problems, such as the low soil fertility and secondary soil salinization. To monitor the change of
soil quality in the developing area can provide the scientific bases for the synthetic agriculture development and the sustainable and rational utilization of land resources. There are many factors affecting the soil quality. In this paper, a mathematical model is developed for selecting the
evaluation indexes of soil quality based on analyzing the theory of related structure of the main component. By using the developed model, 14 indexes are selected from the 24 indexes of the soil quality in the Karamay Agricultural Developing Area, and the selected indexes are tested by hierarchical cluster analysis. Although the two processes of cluster before and after the selection are similar, the indexes and the eigenvalues are reduced after selecting, the contribution of the main component to the total variance is greatly increased, and the result of the main component is made to be more obvious. Moreover, the influence of the abnormal indexes of very few soil samples to the cluster can be avoided, and the cluster results after selecting are closer to the classification standards of soil survey in 1996. These reveal that the selected indexes can basically reflect the main soil properties in the developing area, and the selected results are reliable.