In order to study the evolution of the chemical structural characteristics of coal samples with the increase of the degree of metamorphism, the distribution of functional groups of five coal samples with different degrees of metamorphism was studied by Fourier transform infrared spectroscopy and split-peak fitting technique, and the structural parameters were calculated based on the results. The results showed that the chemical structure of the coal samples with different degrees of metamorphism differed significantly, but the overall trend of the evolution of the samples was similar as the degree of metamorphism increased, i. e., the relatively more active functional groups gradually decreased, the more stable functional groups gradually increased, and the chemical structure of the coal samples as a whole developed towards stability and order. With the deepening of coal sample metamorphism, in terms of hydroxyl functional groups, the free hydroxyl group gradually decreased. At the same time, the hydroxyl-π hydrogen bond gradually increased, and the relative content of hydroxyl self-conjugated hydrogen bond fluctuated within 40% to 55%, which was the main type of hydroxyl hydrogen bond in coal. The overall trend of hydroxyl ether-oxygen bond and ring-conjugated hydrogen bond decreased. In terms of aliphatic hydrocarbon structure, the relative content of methylene in the experimental coal samples was higher than that of methyl and hypomethyl, indicating that the lipid ring structure and lipid chain structure were more developed in coal. At the same time, the structural parameter A(CH₂)/A(CH₃) increased and then decreased, indicating that the fatty chains composed of methyl, methylene and hypomethyl tended to develop in the coal samples with low degree of metamorphism, and started to break in the coal samples with medium and high degree of metamorphism. The overall length of fatty chains tended to increase and then shorten, but the number of branched chains as a whole tended to decrease and then increase. The relative content of C—O in phenols tended to increase and then decrease, and the relative content of aryl ethers and alkyl ethers gradually increased and became the main oxygen-containing groups in anthracite coals. Functional groups in anthracite. In the aromatic hydrocarbon structure, the benzene ring substitution is mainly trisubstituted, and the structural parameters $f^{C}_{ar}$ and DOC gradually become larger, which indicates that the aromatic system in coal increases and the degree of aromatic structure condensation gradually increases, and the degree of aromatic structure condensation in anthracite coal is much stronger than other coal samples.