<p>To investigate the effect of CO₂ retention time on the spontaneous combustion characteristics of gas-fat coal in goaf, the variation patterns of functional group composition, pore structure parameters, and heat release of coal under different CO₂ retention times are analyzed by simultaneous thermal analysis, Fourier transform infrared spectroscopy, and isothermal adsorption experiments. The combustion characteristics are further studied by combining combustion kinetics and thermodynamics theories. The research results indicate that, compared with raw coal, the coal pores expand substantially when the CO₂ retention time is 1–5 days, with the specific surface area increasing by 5.20–12.13%, and the total pore volume increasing by 101.60–328.12%. Methyl and methylene groups slowly oxidize to form hydroxyl groups, with the proportion of hydroxyl groups increasing by 6.86–8.58% and the heat release decreasing by 8.61–19.46%. The coal pores shrink, and the specific surface area and total pore volume are 10.56% and 124.60% higher than those of raw coal when the CO₂ retention time is 5–10 days. Hydroxyl groups undergo condensation and etherification reactions and are largely converted into phenolic alcohol ethers, with their proportion increasing by 1.53% and the heat release increasing by 7.88% compared with raw coal. Taking the CO₂ retention time of 1 day as the baseline, the low-temperature oxidation activity of coal is inhibited when the retention time is 5 times the baseline, and promoted when it reaches 10 times the baseline. With the increase in CO₂ retention time, the combustion reaction rate constant of coal shows a decreasing trend. Meanwhile, both the enthalpy change and entropy change decrease, while the Gibbs free energy change remains greater than 0, showing that the combustion reaction of coal is inhibited. The research results can provide a theoretical basis for the safe application of CO₂ fire prevention and extinguishing technology in goaf.</p>