Once fires occur in a coalfield, large quantities of coal in the coalfield will be baked at high temperatures. The changes and differences in the microscopic and spontaneous combustion properties of coals in high-temperature environments (ambient temperature or even after high-temperature baking) in the fire zone have not been studied yet. In this paper, three types of different-rank coals were baked at five different temperatures to investigate their changes in microcrystalline compositions, functional groups and combustion characteristics. The following results were obtained. The temperature treatment causes damage to the microcrystalline structure of different-rank coals. As the baking temperature rises, the aromatic layer spacing decreases, while the ductility and stacking height gradually increase. The aromatic ether content and the aliphatic hydrocarbon content gradually decline, while the -COOH content goes first and then falls. The spontaneous combustion activities of coals around the fire area gradually weaken with the rise of baking temperature. This research is crucial for revealing the effect of temperature, especially fire baking, on the spontaneous combustion characteristics of coal.