Fourier transform infrared spectroscopy (FTIR) was directly applied to study the decomposition process of corn straw residue (CSR).The result showed that FTIR spectra could indicate the dynamic changes of organic components during the deeomposition process of CSR With the progress of CSR decomposition,hydroxyl, ketonic carbonyl, methyl, methylene, methine and aliphatic compounds decreased, but aromatic compounds increased.This meant that the carbohydrates and aliphatic compounds decomposed quickly and lignin decomposed slowly.The inorganic elements, especially silicon, were reduced from the CSR and accumulated as oxides and some other inorganic elements were reacted with carboxyls to form carboxylates.In the process of decomposition, carboxyl existed as carboxylic ions, most carbohydrates and aliphatic compounds were oxidized to CO₂ and H₂O, the proteins and amino acids were decomposed to CO₂, NH₄⁺,NO₃^- and amides, and the lignin were decomposed to hydroquinones.As far as the differences between the leaf and the stem during the decomposition process of CSR, methoxy increased in the leaf, however, no significant changes were observed in the stem; the organic silicon compounds and lignin decomposed significantly in the leaf, but the change was little in the stem; undecomposed leaf didn't contain carboxylic ions, on the contrary, carboxylic ions existed in undecomposed stem.During the decomposition process of CSR, addition of N fertilizer promoted the decomposition progress of CSR. The chemical analyses showed that the humification index when the leaf and stem were mixed and decomposed was higher than that when the leaf and stem were decomposed separately.