Abstract: In order to master the relationship between the key active groups of weathered coal and oxidized coal at the characteristic temperature of coal spontaneous combustion, this paper takes the fresh coal as the reference coal to compare and analyze the microstructure of weathered coal and oxidized coal. Firstly, the relative content of active functional groups and characteristic structural parameters of weathered coal and oxidized coal in the initial state were analyzed by Fourier transform infrared spectroscopy, the variation laws of four main active functions under characteristic temperature were determined, and the differences of different active groups between weathered coal and oxidized coal were semi quantitatively analyzed. The key active groups affecting the difference of natural ignition between weathered coal and oxidized coal are revealed. Through the programmed temperature rise experiment of coal spontaneous combustion, the release characteristics of index gas concentration of weathered coal and oxidized coal were analyzed, and the evolution and migration of key functional groups at characteristic temperature were verified. The results show that the content of CO produced by oxidized coal was higher than that of weathered coal due to the different content of C-O-C in oxygen-containing functional groups, while the content of C2H6 produced by weathered coal was higher than that of oxidized coal due to the different asymmetric stretching vibration of methyl and methylene in aliphatic hydrocarbons.