Abstract: Based on thermodynamic equilibrium calculations, this study examines the absorption of SO₂ by both the slurry and clear liquor of a magnesium sulfite and sodium sulfite mixture, respectively. The results show that pure magnesium sulfite slurry has an initial pH of 8.99, but the equilibrium concentration of sulfite capable of desulfurization in the solution reaches only 0.056 mol/L. In contrast, when magnesium sulfite, sodium sulfite, and magnesium hydroxide are mixed, the initial pH increases with higher sodium sulfite concentrations, while the final pH after the sulfite desulfurization reaction decreases to 4.55. The mixed slurry of magnesium sulfite and sodium sulfite significantly increases the sulfite concentration in solution, thereby maintaining a high SO₂ absorption capacity even as the pH decreases. If a clear mixed liquor of magnesium sulfite and sodium sulfite is used, no solid precipitation forms during the desulfurization, thus avoiding pipeline blockage. Nevertheless, the sodium sulfite concentration in the clear liquor must remain sufficiently high to ensure adequate SO₂ absorption capacity, as the desulfurization capacity declines significantly when the pH falls below 6. Based on these thermodynamic analyses, a two-stage absorption and two-stage regeneration process is proposed for the magnesium sulfite sodium sulfite clear liquor desulfurization system.