Abstract: Focusing on the phenomenon of CO content exceeding the standard in Kailuan mining area, based on proximate analysis, ultimate analysis, R_max, FT-IR, and scanning electron microscope (SEM) analysis of 22 typical coal samples, the authors analyzed the macromolecule structure evolution and the origin of CO. The results show that with the increase of R max, H/C increases first then decreases; content of C-O and C=O is high; with the increase of R max, f_a increases first then decreases, 2(R-1)/C decreases first then increases, the inflection points is at 0.8%; the pore type of the coal sample is inter-grain pore. It is considered that the CO of Kailuan mining area was formed from chemical combination of free radicals resulted side chains breaking by the actions of tectonic stress of different direction during the process of metamorphism.