In order to explore the oxidation characteristics of CaSO₃ in the desulfurizer slurry mixed with pellet desulfurization ash and limestone powder, the oxidation rate under different oxidation time, oxygen flow, proportion of pellet desulfurization ash and CaSO₃ mass fraction is determined by setting up an oxidation test device to simulate the reaction conditions of wet desulfurization in power plants, and the influence of different experimental conditions on the oxidation rate of CaSO₃ is analyzed. The results show that the increase of oxidation time and oxygen flow would promote the oxidation of CaSO₃ under acidic environment; the prolongation of oxidation time is more favorable than the increase of oxygen flow for the oxidation of CaSO₃. The lower percentage of desulfurization ash and CaSO₃ mass fraction is favorable for CaSO₃ oxidation rate; the suitable oxidation time and oxygen flow are different for different pellet desulfurization ash. The conclusion can provide theoretical and technical support for improving the oxidation of CaSO₃ in mixed desulfurizer slurry to play the role of pellet desulfurization ash in wet desulfurization.