Spectroscopic measurement(Fourier transform infrared differential spectroscopy,Carbon 13 nuclear magnetic resonance spectrometry,Matrix-assisted laser desorption/ionization-time of flight mass spectrometry)and elemental analysis were performed of fulvic acids(FA)extracted from soils applied with corn plant residues.The results show that after corn plant residues were applied into the soil,C,H and N contents increased,O content decreased,and rat ios of C/H,O/C and C/N all declined in soil FA.The carboxyl groups and aromatic carbon were comparatively lower,suggesting a low degree of oxidation and a low aromaticity of FA.Structural changes in soil FA showed a trend of becoming simpler in structure and smaller in molecule size.At the same time,amide,alkyl C and O-alkyl C contents increased significantly.Combining capacity of soil FA with inorganic minerals was gett ing weaker.Carboxylic groups in soil FA were turning from carboxylates into free carboxyls.Polysaccharide components in FA also increased The changes in composition and structure of FA varied from treatment to treatment.