The kinetics of sulfite oxidation in the simultaneous desulfurization and denitrification of the oxidation-absorption process was investigated with a bubbling apparatus under the conditions of varying pH, sulfite concentration, nitrite concentration, temperature, and air flow. The results indicate that the oxidation of sulfite is promoted dramatically by mixing with nitrite, due to the decline of the apparent energy of activation and the initiation of nitric dioxide decomposition by nitrite. An increase of the nitrite concentration, the air flow, the reaction temperature, or the pH supports the decomposition of nitrite and the production of nitric dioxide, thus leading to an enhancement of the sulfite oxidation rate. A kinetic model is established according to the experimental results. A satisfactory agreement between the calculated and the experimental values is obtained.