Abstract: During coal storage and open-air stockpiling, photooxidation is the key precursor step triggering spontaneous combustion. However, the molecular structural regulation mechanism of the pre-oxidizing temperature on the generation of hydroxyl radicals—the core active radical species in photooxidation—is still unclear. The regulation mechanism of coal photo-oxidative hydroxyl radical generation by preoxidation temperatures ranging from 30−150 ℃ is studied through Fourier Transform Infrared Reflection, Electron Paramagnetic Resonance , hydroxyl radical trapping experiments, and mathematical analysis. It is found that the low-temperature preoxidized coal samples at 30–90 ℃ are rich in hydroxyl groups and aliphatic side chains; at high temperatures of 120–150 ℃, the aliphatic side chains fracture extensively, and aromatic structures become significantly enriched. The hydroxyl content in photooxidation exhibits exponential decay, determining a self-limiting rule of active site consumption and aromatic structural stability, i.e., the reduction in oxidizable sites and the intensification of aromatization jointly inhibit the reaction driving force, essentially a restraint on the reaction process imposed by the self-reinforcing structural stability of the oxidation process itself. Pre-oxidation temperature governs the stability of persistent free radicals (PFRs). Low-temperature preoxidized coal samples exhibit low aromatization levels, making PFRs prone to react and consume with aliphatic side chains, with less stability, whereas high -temperature is the opposite. Under the light, the hydroxyl radical spin density is positively correlated with the pre-oxidation temperature: the hydroxyl radical spin density in high-temperature coal samples reaches 10⁸–10⁹ mm⁻³, with a response time of 10 min; the hydroxyl radical spin density in low-temperature coal samples is below 10⁸ mm⁻³, requiring 20 min for response. Mechanistic analysis indicates that high temperature enhances hydroxyl radical generation through two pathways: one is to promote the aromatization to stabilize the electronic environment of PFRs, reducing non-specific inactivation; the other is to push for aliphatic hydrocarbon fracture to increase active sites, enhancing the transformation from photo-induced PFRs to hydroxyl radicals. Although low-temperature coal has many initial active sites, the instability of PFRs limits conversion efficiency. A mechanism chain linking “pre-oxidation temperature–molecular structure–PFRs stability–hydroxyl radical generation” is further established, clarifying the interrelationship among temperature regulation, structural evolution, and radical active species. These research outcomes refine the multiscale correlation theory of spontaneous combustion caused by coal photooxidation, providing critical theoretical support for preventing and controlling spontaneous combustion in stored and open-air coal.