Abstract: To investigate the impact of introducing CO₂ on the reaction between coal and oxygen, this study analyzed the variation patterns of the relative contents of active groups in coal. As a result, the active group that is most significantly influenced by the CO₂ condition was identified. The coal sample from Zhangjiamao coal mine was chosen as the research object. Experiments were carried out using different volume fractions of CO₂ atmosphere, and coal samples within the temperature range of 100−200 ℃ were selected for Fourier transform infrared spectroscopy experiments to explore the variation law of the relative content of various active groups under different volume fractions of CO₂ atmosphere. Based on the grey correlation analysis of the correlation between CO₂ and active groups, the types of key functional groups affected by the increase in the volume fraction of CO₂ were studied. The results show that under the influence of the addition of CO₂, the infrared spectra of each functional group present different peak area variation characteristics compared with the results under air conditions. Among them, with the increase in temperature, the hydroxyl group shows a decreasing trend, among which the intramolecular hydrogen bonds represented by hydroxyl self-association hydrogen bonds and hydroxyl-π hydrogen bonds decrease more significantly; the stretching vibrations of methyl and methylene in aliphatic hydrocarbons show a slight increase followed by a decrease trend, while the angle change vibration shows a continuous decrease trend; in oxygen-containing functional groups, carbonyl, ether bonds, and carboxylic acids all show an increasing trend; in aromatic hydrocarbons, it is mainly manifested that the increase in 3-substitution and 5-substitution is more obvious, and the C=C stretching vibration in the aromatic ring shows a decreasing trend with temperature. The analysis of the variation trend of the relative content of active groups reveals that although the relative content changes of each active group are different, the variation trends of each active group under different experimental conditions of CO₂ volume fractions are basically the same. This suggests that the introduction of different volume fractions of CO₂ does not alter the reaction process of functional groups in coal. The results of the correlation analysis show that the ranking of the types of functional groups with the greatest influence on the coal-oxygen reaction by the addition of CO₂ is: oxygen-containing functional groups > hydroxyl groups > aliphatic hydrocarbons > aromatic hydrocarbons.