Abstract: In order to investigate the influence of gas mixture (O₂/N₂ and O₂/N₂/CO₂) on the spontaneous combustion characteristics of coal, synchronous thermal analyzers, temperature programmed gas chromatography/infrared spectrometers were used to study the characteristic temperature, thermal effect/indicator gas, and functional group changes of coal under gas mixture. The results show that under O₂/N₂ atmosphere, with the increase of N₂ volume fraction, the characteristic temperature point lags behind, TG, DTG, DSC all shift towards high temperature, heat release decreases, activation energy during combustion stage increases, final oxygen consumption and CO volume fraction of coal decrease, hydroxyl groups in coal increase, and the content of aliphatic hydrocarbons, oxygen-containing functional groups, and aromatic hydrocarbons shows a decreasing trend; under O₂/N₂/CO₂ atmosphere, as CO₂ increases, the characteristic temperature point shifts backward, the heat release decreases, the activation energy during the combustion stage decreases, the oxygen consumption and CO volume fraction both decrease, hydroxyl and fatty hydrocarbons increase, and the content of oxygen-containing functional groups decreases; when the volume fraction of O₂ is the same, the peak weight loss rate, oxygen consumption, and CO volume fraction in the O₂/N₂/CO₂ mixture are all lower than those in O₂/N₂; −OH is easily oxidized and undergoes dehydration reaction. Coal releases less heat in the initial stage of the reaction, but rapidly increases in the later stage. CO is mainly generated by −C=O.