Abstract: Taking 30 typical soil profiles in the karst mountainous areas of Guizhou as the research object, this paper collected soil samples, measured the contents of different forms of iron oxide, calculated the corresponding weathering index, analyzed the relationship between the contents of different forms of iron oxide, weathering index and the differentiation of soil types, and discussed the indicative effect of iron oxide characteristics on the differentiation of typical soil types in the karst mountainous areas. The results showed that free iron oxide was its main form in the soil (26.62-75.99 g kg⁻¹). Most of the soil samples had the iron activity degree < 30%, free degree ≥ 50%, and free iron oxide ≥ 30 g kg⁻¹ in the middle stage of desilication and aluminum enrichment. The complex iron oxide and complexation degree of soil showed a strong spatial heterogeneity. There were significant differences (P < 0.05) in iron oxide form and weathering index (except crystalline iron oxide and degree of complexation) among different types of Calcareous soil based on the Chinese soil genesis classification. With the increase of crystalline iron oxide, crystallized degree and free degree, the activity degree was decreased, and the weathering degree of soil was increased gradually. The evolution of soil types was from Brown Lime soil to Yellow Lime soil and then to Red Lime soil. In the Chinese soil taxonomy (soil order, soil group), the iron oxide forms and weathering index (except crystallinity) were quite different among soil classes, subgroups and groups. With the increase of crystalline iron oxide, free degree and crystal gel rate, the activity degree was decreased, and the weathering degree of soil was gradually deepened. There was an evolution trend of soil class from leaching soil to iron rich soil and from calcareous soil to iron wet leaching soil.