Abstract: In order to explore the change characteristics of organic group chemical structure of coal after liquid CO₂ leaching and acidification, liquid CO₂ leaching and acidification coal sample experiments were carried out on anthracite at 25 ℃ and 3 MPa. The changes of functional groups in the process of CO₂ leaching and acidification were analyzed by Fourier infrared spectroscopy (FTIR). The results show that swelling, dissolution, extraction, bond dissociation and substitution are the main reactions in the liquid CO₂ leaching process, and different types of addition reactions occur in the liquid CO₂ acidification process besides the above reactions. The above reactions result in dissolution and recombination of different types of functional groups, small molecule phase organic matter and large molecule phase organic matter. In addition, the aromaticity and condensation degree of coal samples are improved after liquid CO₂ leaching and acidification.