It’s a gas-liquid-solid three-phase reaction system in the reactor for flue gas desulfurization using pyrolusite pulp. Based on the two-film mass transfer theory and shrine core model, the macro-kinetics of flue gas desulfurization using pyrolusite pulp in a double magnetic stirred reactor were investigated. The effects of diffusion in solid film, surface chemical reaction, diffusion in liquid phase and gas phase of the process, have been carried out to distinguish the control step of the process. It was observed that SO2 absorption efficiency increased with the decreasing of pyrolusite particle size and varied gently when the pyrolusite particle diameter decreased to 0.18mm. SO2 absorption efficiency increased not significantly along with the increase of temperature and the liquid phase stirring speed but increased significantly along with the increase of the gas phase stirring speed. Experiment results showed that under simulated industrial conditions, gas phase diffusion was the control step compared to other related factors, given that pyrolusite particle diameter was kept below 0.1mm.