Abstract: In this paper, lean coal, fat coal and gas coal were taken as the research objects to deeply study the macroscopic gas release law and microstructural changes of coking coal during low temperature oxidation. The gas release laws were obtained by heating and isothermal oxidation and the structure of coals was characterized by N₂ adsorption, scanning electron microscopy equipped with energy dispersive X-ray analysis (SEM-EDS) and infrared spectroscopy (FT-IR). The results of constant temperature experiment showed that a small amount of the CO generated at a certain temperature produced by the thermal decomposition of coal itself, and the majority came from the decomposition of carbon-oxygen complexes produced by oxidation reaction. N₂ adsorption and SEM characterization results indicated that at 95 ℃, the destructive effect on coal structure was minimal, while at 190 ℃, the cracks on coal surface increased and the degree of pulverization became larger. The total volume and average pore diameter increased, while BET surface area decreased due to the blockage of some oxidation products. Al and Si elements were detected on the surface of coal, therefore it could be inferred that the attached particles contained Al₂O₃ and SiO₂. FT-IR characterization result showed that during the low temperature oxidation process, −OH, −CH₃ and −CH₂− reacted with oxygen forming unstable carbon-oxygen complexes such as C＝ O, −COOH and ether bonds, which were further decomposed into CO, CO₂ and other gases. The thermodynamic feasibility of the proposed gas generation mechanism was verified by HSC Chemistry 6.0. In addition, the higher the volatile content of coal contained, the smaller the proportion of aromatic structures and thus the more developed pore structures, resulting in a more frequency of oxidation and the spontaneous combustion occurred.