Abstract: Sulfur dioxide (SO2) is one of the main acidic pollutants in coal-fired flue gas. Its efficient removal is of great significance for achieving clean coal utilization and regional air pollution control. To address the issues of traditional activated coke (AC) such as limited adsorption capacity, insufficient chemical activity, and significant performance degradation after multiple regenerations during low-concentration flue gas desulfurization, Fe-modified activated coke (FeAC) was prepared by combining KOH activation and iron salt impregnation. Its SO2 removal performance, cyclic regeneration behavior, and adsorption kinetic characteristics under medium-low temperature conditions were systematically evaluated, and the underlying mechanism was analyzed using multiple characterization techniques. Under simulated flue gas conditions (120 °C, with O2 and water vapor), FeAC exhibited significantly superior desulfurization performance compared to unmodified AC. The initial breakthrough sulfur capacity of fresh unmodified AC was only 3.22 mg/g, while that of FeAC increased to 26.45 mg/g, representing an approximately 8-fold improvement in desulfurization capacity. After multiple in-situ thermal regenerations, the sulfur capacity of unmodified AC gradually degraded, dropping to 3.82 mg/g after the fourth regeneration. In contrast, although the sulfur capacity of FeAC showed a decreasing trend during cycling, its stable sulfur capacity remained at approximately 9 mg/g, which was significantly higher than the initial desulfurization level of unmodified AC. This indicates that Fe modification effectively enhanced the long-term serviceability of the material. Characterization results further revealed the desulfurization mechanism of FeAC. Scanning Electron Microscopy (SEM) and Fourier Transform Infrared Spectroscopy (FTIR) analyses demonstrated that uniformly distributed Fe-based active components were formed on the surface of modified AC, and sulfate deposits were generated after SO2 adsorption. X-ray Photoelectron Spectroscopy (XPS) results showed that sulfur on the surface of the adsorbed sample mainly existed in the form of high-valent sulfur (S6+), and the Fe2+/Fe3+ redox couple maintained dynamic equilibrium during the reaction. This suggests that Fe-based active sites can catalyze the conversion of SO2 to thermodynamically stable sulfate species. Comprehensive analysis indicates that the high desulfurization performance of FeAC primarily stems from chemisorption and catalytic oxidation mechanisms dominated by surface iron species, rather than relying solely on physical pore adsorption. Adsorption kinetic analysis showed that the SO? adsorption process of unmodified AC indicates that the desulfurization process of unmodified AC is dominated by physical adsorption accompanied by limited surface reactions. In contrast, the adsorption behavior of FeAC was significantly different: the Bangham model showed a higher goodness of fit to the experimental data (R2 = 0.9982), reflecting the presence of unevenly distributed high-energy chemisorption sites on its surface. Thus, the SO2 removal process of FeAC is co-dominated by chemisorption and catalytic reactions. The results of this study demonstrate that this composite modification can significantly enhance the SO2 removal capacity and regeneration stability of activated coke, providing a promising material solution for the efficient and renewable removal of SO2.