Abstract: In order to investigate the evolution law of the functional groups of pre-oxidized coal samples, lignite from Liujia and Sitai, bituminous coal from Tongxin and anthracite from Baijigou were pre-oxidized at 50 ℃, 120 ℃ and 200 ℃ for 6 h. Fourier transform infrared spectrometer was used to test the infrared spectrum of both original and pre-oxidized coal samples. The evolution law of functional groups on the coal surface was obtained. the results showed that: pre-oxidation did not change the type of functional groups, which only changed the amounts of functional groups; The higher is the pre-oxidation temperature, the more functional groups of -OH were involved in the reaction. The absorbance of the -OH decreased 51.43% after the pre-oxidization at 200 ℃, which suggested that the pre-oxidation had more effects on the low metamorphic degree coal; as the pre-oxidation temperature increased, the functional groups of -CH₂-, -CH₃ and -C=O increased first, and then decreased. For coal samples pre-oxidized at 50 ℃, the amounts of -CH₂-, -CH₃ and -C=O increased after pre-oxidation; for coal samples pre-oxidized at 120 ℃ and 200 ℃, the amounts of -CH₂-, -CH₃ and -C=O decreased after pre-oxidation. When the pre-oxidized coal samples were re-oxidized, compared with the original coal samples, the coal samples pre-oxidized at 50 ℃ generated more gases of CO, CO₂, C₂H₄ and C2H6 at a lower temperature, while the coal samples pre-oxidized at 120 ℃ and 200℃ generated less gases at ahigher temperature.