In order to find the rules of selecting organic desulphurization additives, eight kinds of organic acids with different pKa values, carbon chain lengths, and functional groups were discussed. As a result, three screening rules can be obtained for selecting organic desulphurization additives: firstly, the pKa value of organic acid should be between 4.21 and 4.83; then short carbon chain was better for SO2 removal; finally, organic acid with functional group was better than linear chain. Moreover, organic acids increased the desulphurization efficiency by promoting the oxidation of SO32- and accelerating the gas-liquid mass transfer and dissolution rate of SO2.