Abstract: The Fourier transform infrared spectroscopy（FTIR） experiment and peak fitting technology were used to perform qualitative and quantitative researches on the functional groups of three coal samples with different levels of metamorphism to calculate and analyze infrared spectrum structure parameters. The results of the study show that as the deterioration of coal samples deepens, the hydroxyl functional groups gradually increase, the content of hydroxyl-N and ring hydrogen bonds decreases, and the content of hydroxyl-π increases; in aliphatic hydrocarbons, the methyl content increases, while the methine content decreases. The oxygen-containing functional groups gradually decrease, and C=O shows a downward trend. The content of carboxyl groups is the highest in low-grade coals, and there are almost no carboxyl groups in high-grade coals. Aromatic hydrocarbons gradually decrease, and aromatic hydrocarbons are mainly substituted by three or four. As the degree of metamorphism increases, the length of fatty side chains becomes shorter, the degree of branching increases, the maturity of organic matter increases, and the carbon skeleton becomes softer; coal metamorphism is a process of deoxidation and carbon enrichment. The aromatic carbon ratio, aromatic hydrogen ratio, aromatic degree and condensation degree of coal with high metamorphic degree are higher, which makes the arrangement of structural units in coal more regular and orderly and the structure more stable.