To provide theoretical instructions for experiments and industrial application of regenerative flue gas desulfurization by sodium phosphate solution, the properties of phosphate solution and multiple buffer solution system of phosphoric acid-sulfurous acid-sodium salts formed from the desulfurization process were analyzed using the theory of multiple buffer solution combined with the chemical equilibrium principle and computer numerical calculation methods. The influence of pH and phosphate concentration on the distribution coefficient and buffer capacity was calculated and validated by experiments. Results indicate that the distribution coefficient of the species in buffer solution only varied with the solution pH value. The experimental buffer performance was similar to the theoretical value.