Abstract:Lou soil and yellow loamy soil, which occupy larger proporation of the loess area were employed in this paper. Under the condiation of long-term application of chemical and organic fertilizers, chemical pyrolytic and speotral properties of soil humic acid were studied. The results showed that long-term application of chemical or organic fertilizers, the nitrogen content of humic acid was increased while the carbon content was decreased. Soil humic acid had more aliphatic groups and fewwer aromatic groups, the degree of polymerization decreased and the molecular became simple and active. Meanwhile, the effect of organic fertilizer on humic acid was greater than that of chemical fertilizer.