Abstract: To study the physical and chemical reaction characteristics during the spontaneous combustion process, and analyze the key controlling factors of coal gangue spontaneous combustion, industrial analyzers, elemental analyzers, sulfur content testers, coal spontaneous combustion tendency testers, Fourier transform infrared spectrometers, and thermogravimetric analyzers are used to evaluate coal gangue from eight coal mines: QX (Qinxin), XS (Xinsheng), XZ (Xinzhuang) from Qinshui Coalfield, SJH (Sanjiaohe) from Huoxi Coalfield, FM (Fumin) and BPW (Baopingwan) from Dongsheng Coalfield, SGT (Shigeitai) from Shenfu Coalfield, and DYG (Dayugou) from Xinggong Coalfield, and a risk assessment model for coal gangue spontaneous combustion is established. The results show that FM, BPW, SGT, and DYG coal gangues have high ash content but relatively low volatile matter and fixed carbon, which is consistent with the elemental analysis results. Moreover, the spontaneous combustion mechanism of coal gangue is considered to be a coupling of the coal combustion mechanism and pyrite combustion mechanism, with the essence of coal gangue spontaneous combustion being an oxidation process. The pyrite sulfur content, physical oxygen absorption, and the content of aliphatic C−H active components are relatively higher in QX, XS, XZ, and SJH coal gangues. Thermogravimetric analysis reveals the ignition point temperature and the activation energy required for the thermal decomposition stage of the gangue; the BPW coal gangue has relatively low ignition point temperature and activation energy for the thermal decomposition stage. The six key controlling factors for spontaneous combustion of coal gangue are thus identified: ash content, pyrite sulfur content, physical oxygen absorption, active functional group content (aliphatic C−H components), ignition point temperature, and activation energy of spontaneous combustion reactions.