【Objective】This study aimed at exploration of effects of application of organic materials on composition of humic acid functional groups in primary saline-alkali soils.【Method】A field experiment was carried out in a field of original saline-alkali soil in Da""an City, Jilin Province. The experiment was designed to have CK and four treatments, that is, CK (control without application of any organic material), Treatment KL (application of granular straw), Treatment JG (application of normal corn stalk), Treatment MC (application of forage grass), and Treatment YF (application of sheep manure). Humic acids extracted from the soil of each treatment were analyzed with a fourier transform infrared spectroscopy (FTIR) and the principal component analysis technique and infrared spectra obtained were characterized relative to treatment. 【Result】Results show that the treatments increased the relative content of fatty carbon and aromatic carbon in soil humic acid, but reduced the content of carboxyl carbon as compared with CK. With the exception of KL, all the treatments increased the relative content of amino compounds in soil humic acid. In addition, all the treatments increased the ratios of aliphatic carbon/carboxyl carbon and aliphatic carbon/aromatic carbon in soil humic acid, which indicates that the application of organic materials reduces the structural condensation degree and oxidation degree of soil humic acid, while enhancing aromaticity. The structure of humic acid also tended to be aliphatic, simple, and young. Comparison between KL and JG shows that KL was higher than JG in relative content of aliphatic carbon in humic acid, but lower in relative content of carboxy-carbon and aromatic carbon in humic acid. Furthermore, JG increased the relative content of amino compounds in soil humic acid, while KL slightly reduced it. Judging from the ratio of I₂₉₂₀/I₁₇₂₀ and I₂₉₂₀/I₁₆₂₀ in humic acid, KL treatment is more conducive to formation of humic acid, younger, simpler and more aliphatic in structure in the soil. The principal component analysis indicates that the applied organic materials are one of the main sources of aliphatic carbon, aromatic carbon and amino compounds in soil, which provides a basis for exploring sources of humic acid functional groups. Via FTIR infrared spectroscopy, it was found that soil humic acid functional groups varied in composition with treatment or type of the organic material applied. This provided a theoretical basis for studying mechanism of the application of organic materials affecting humic acid properties in the soil.【Conclusion】In summary, the applied organic materials are one of the major sources of aliphatic carbon, aromatic carbon and amino compounds in the soil. As affected by the application, humic acid in the soil was lowered in structural condensation degree, oxidation degree and aromoticity, while enhanced in aliphaticity. Consequently the humic acid tended to be aliphatic, simple, and youngin structure. The effects on composition of humic acid in the soil varied with treatment or type of the organic material applied. As such, granulated straw is more conducive to the formation of humic acid, younger, simpler and more aliphatic in structure in the soil.