Abstract: To address the issue that traditional aqueous inhibitors are prone to dehydration and deactivation caused by high geothermal temperatures and strong air leakage in deep coal mine goafs, which makes it difficult to persistently inhibit coal spontaneous combustion(CSC), a deep eutectic inhibitor (DEI) based on a deep eutectic solvent as the liquid carrier and compounded with vitamin C (VC) and propyl gallate (PG) was proposed. The isothermal drying method combined with the Fick diffusion model was used to define a relative water retention index to evaluate the liquid domain stability of DEI at high temperatures. Low-field nuclear magnetic resonance (NMR) technology and a C600 microcalorimeter were utilized to investigate the infiltration and sealing laws at the pore interfaces and the oxidation exothermic characteristics of DEI on coals with different metamorphic degrees. Furthermore, density functional theory was applied to reveal the synergistic scavenging mechanism of VC and PG on typical active free radicals in coal. The results show that DEI effectively binds water molecules and delays water evaporation through its hydrogen bond network. The moderate evaporation of water at a high temperature of 80–100 ℃ induces the reconstruction of the hydrogen bond network to form a high-strength three-dimensional network structure. This enables its relative water retention index to reach a peak value of 0.78, demonstrating excellent high-temperature liquid domain stability. NMR results indicate that DEI can penetrate and reconstruct the pore network of coal, transforming the fluid in coal from a free state to a strongly bound state that is difficult to detach. The proportion of the bound water area increases to 70%−80%, and the bound porosity area of the first peak of micropores is enlarged, realizing the persistent sealing of primary micropores. Thermodynamic analysis demonstrates that after the DEI treatment, the endothermic termination temperatures of coal samples with varying metamorphic degrees are delayed to 174.5−183.6 ℃, and the corresponding phase-transition heat absorption is substantially increased by 161.39%−421.89%. Furthermore, the heat release during the low-temperature oxidation stage is reduced by 12.62%−34.84%, and the apparent activation energy in the temperature range of 200−300 ℃ is enhanced by 40.52%−100.67%. Quantum chemical calculations reveal that VC and PG can effectively scavenge the active free radicals during coal oxidation. Additionally, VC enhances the free-radical scavenging activity and persistence of PG through electron induction and intermolecular charge transfer, exhibiting a synergistic antioxidant effect. The research results provide theoretical and technical support for the persistent inhibition of CSC in deep coal mine goafs.