Abstract: In order to study the transformation law of the most essential active groups in the process of coal spontaneous combustion and low-temperature oxidation, the Fourier in-situ infrared measurement technology was used to obtain the distribution of the main functional groups of the raw coal, and the key active groups in the coal were obtained by peak fitting. The content changes during the heating process under different atmospheres were compared, and the active group conversion curve representing the intrinsic coal-oxygen recombination reaction was obtained by using the subtraction map. The results show that the content of -CH₃ and -CH₂- in the air atmosphere decreases overall, and the content conversion rate of -COOH with the increase of temperature is less than that of C=O; the net difference of the content change of -COOH under pyrolysis in nitrogen atmosphere is the largest; in the coal-oxygen recombination reaction, the overall decrease in the content of active groups is due to the fact that the consumption rate of the oxidation reaction is greater than the production rate; the coal oxidation reaction rate began to increase gradually from 60 ℃to 70 ℃, and it was found that the decrease of the overall content of four key active groups provided conditions for the low-temperature oxidation reaction of coal samples.