Elemental composition,molecular structure,and physical and chemical properties of Ca bound and Fe/A1-bound humus in soil were determined by chemical and instrumental analyses.Results showed that the contents of C,H and N were higher in Fe/Al-bound humus than in Ca-bound humus,while the ratios of C/H and C/N were higher in Ca-bound humus.The aromaticity of humic acid in Fe/AI-bound complex was higher than in Ca-bound complex,but that of fulvic acid was higher in Ca-bound complex.Fe/Al-bound humus had the higher thermal stability and the stronger affinity for coordinating metal ions than Ca-bound humus.