Blast furnace sludge (BFS) exhibits a strong sulfur-fixing ability due to the large amount of metal oxides, such as Fe2O3, CaO, SiO2, and Al2O, that it contains. In this study, the influence of BFS on SO2 emissions and the sulfur-fixing mechanism is studied in the coal combustion process. The results show that the SO2 emission peak values decrease with the increase of BFS mass percentage and that the sulfur-fixing ratio increases to 89% when the BFS mass percentage reaches 10% at 900 degrees C. The sulfur-fixing mechanism predicts that the multicomponents of BFS favor the formation of a stable sulfate (3CAO(3)center dot Al2O3 center dot CaSO4) and reduce the rapid decomposition of CaSO4 coated by thermally stable sulfur compounds such as CaFe3(SiO4)(2)OH. These results indicate that BFS, as a sulfur-fixing agent, is cheap and highly efficient in controlling SO2 emissions during coal combustion processes.