Forced oxidation of calcium sulfite aqueous slurry is a key step for the calcium-ba sed flue gas de sulfurization (FGD) re sidue. Experiments were conducted in a semi-batch system and a continuous flow system on lab scales. The main reactor in semi-batch system is a 1000ml volume flask. It has five necks for continuous feeding of gas and a batch of calcium sulfite solutionPaqueous slurry. In continuous flow system, the main part is a jacketed Pyrex gla ss reactor in which gas and solutionPaqueous slurry are fed continuously. Calcium sulfite oxidation is a series of complex free2radical reactions. According to experimental re sults and literature data, the reactions are influenced significantly by mangane se as catalyst. Atlow concentration of mangane se and calcium sulfite, the reaction rate is dependent on 115 order of sulfite concentration, 015 order of mangane se concentration, and zero order of oxygen concentration in which the oxidation is controlled by chemical kinetics. With concentrations of calcium sulfite and mangane se increa sing, the reactions are independent gradually on the constituents in solution but are impacted by oxygen concentration. Mangane se can accelerate the free-radical reactions, and then enhances the mass transfer of oxygen from ga s to liquid. The critical concentration of calcium sulfite is 01007molPL, mangane se is 10-4 molPL, and oxygen is of 012-014atm.