Abstract: Coal spontaneous combustion results from synergistic heat release and accumulation through multi-step parallel reactions, with its exothermic characteristics closely related to the evolution of microactive structures. To reveal the multi-step parallel reaction pathways of coal spontaneous combustion, the evolution patterns of functional groups and free radicals were investigated using differential scanning calorimetry, in-situ Fourier transform infrared, and electron paramagnetic resonance experiments during the oxidation and heating process of four coal samples (SYS, ZJM, YZ, LF) with varying degrees of metamorphism. The findings reveal five concurrent reactions during coal spontaneous combustion: dehydration and devolatilization, oxygen adsorption, oxidative decomposition, gaseous combustion, and solid-phase combustion. The superimposed competition of the reaction sequence is related to the variation of the heat release curve and the shift of the characteristic temperature points. The degree of metamorphism influences the distribution of active structures, thereby affecting the oxidation and spontaneous combustion reaction pathways of coal. As the degree of metamorphism increases, the oxidative decomposition temperature of coal samples decreases, while the ignition point temperature becomes delayed. The influence of different parallel reaction sequences on heat variation during coal spontaneous combustion varies significantly. The contribution of physical reaction sequences, such as dehydration and devolatilization, and oxygen adsorption, to the overall heat change is minimal, accounting for approximately 2%. Specifically, oxidative decomposition accounts for 67.4% of the heat release in SYS coal, whereas gas-phase and solid-phase combustion sequences dominate in ZJM, YZ, and LF coals. ZJM and YZ coals exhibit double exothermic peaks due to the superposition of exothermic reaction sequences. While an increased heating rate delays characteristic temperatures, it enhances combustion intensity. Qualitative and quantitative analyses of functional groups and free radicals reveal the types of parallel reactions and synergistic mechanisms. In the initial stage, hydroxyl and aliphatic groups react with physically adsorbed oxygen to form hydroperoxides —OOH. Free radical concentrations initially decrease before rising, and the heat flow curve shows a minor endothermic peak. As the temperature rises, the oxidative decomposition reaction takes the dominant position. The secondary ethyl bond with hydroxyl groups at the α position reacts with oxygen to form ether bonds, and the peroxide decomposes in large quantities leads to an approximately 1.8-fold increase in radical concentration. Notably, ZJM and YZ coals with medium rank display shoulder peaks in their heat flow curves due to exothermic oxidative decomposition. During medium-high temperature stages, peroxide precursors derived from aromatic ring-adsorbed oxygen undergo cleavage to generate carbonyl groups, with aliphatic chain breakage pushing free radical concentration to its peak. In the high-temperature stage, persistently high C=O absorbance and 60% attenuation of aromatic —CH groups confirm gaseous combustion dominance. This study elucidates the parallel reaction sequences and the evolution of micro-active structures, identifying the reaction pathways and key exothermic functional groups in coal spontaneous combustion.