Abstract: Aiming at the problems of strong hygroscopy, easy decomposition and deactivation, and poor storage stability existing in traditional inhibitors, a novel polyethylene glycol (PEG)-based composite microcapsule inhibitor was developed to improve its environmental stability and inhibition effect on coal spontaneous combustion. Taking the composite system of citric acid (CA) and ammonium polyphosphate (APP) as the core material and polyethylene glycol 20000 (PEG20000) as the wall material, the optimal mass ratio of core material was determined as m (CA)∶m (APP) = 1∶5 via screening with a cone calorimeter, and microcapsule inhibitors with core-wall ratios of 1∶1, 1∶2, 1∶3 and 2∶1 were prepared by the melt-dispersion condensation method. The characterization results of scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) showed that a continuous colloidal PEG film was formed on the surface of the microcapsules, and only the wall material elements were detected in the EDS spectra, which confirmed that the core material was successfully encapsulated by PEG20000. The results of thermogravimetric-differential scanning calorimetry (TG-DSC) experiments indicated that the sample with a core-wall ratio of 1∶1 (B2) exhibited the best inhibition performance: its critical temperature t₁ and dry cracking temperature t₂ were increased by 24.95% and 40.22% compared with raw coal, the thermal equilibrium temperature was delayed by 19.45 ℃, the heat absorption capacity was increased by 357.00 J/g, and the heat release capacity was reduced by 898.53 J/g, which significantly delayed the exothermic process of coal oxidation. The results of constant temperature and humidity experiments (RH=70%/60%, 25 ℃) showed that the moisture absorption rate of the B2 sample was reduced by 20.33% and 19.87% compared with the core material inhibitor, respectively, indicating a significant improvement in its environmental stability. Further analysis via programmed temperature rise and Fourier transform infrared spectroscopy (FTIR) demonstrated that the maximum CO generation rate of the coal sample treated with the B₂ sample was reduced by 72.78% compared with raw coal, with the inhibition rate reaching 70.09% at 100 ℃; meanwhile, the peak area proprtions of aliphatic hydrocarbon groups (–CH₃/–CH₂–) and hydroxyl groups (–OH) were reduced by 2.38% and 3.51% compared with raw coal, respectively, while the peak area proprtions of ether bonds (C–O) was increased by 5.73%.