The present paper investigates the simultaneous removal and synergistic effect of SO₂ and NOx in natrium-alkali solutions in a countercurrent packed column in continuous flow mode. On the basis of high SO₂ removal efficiency, the NOx removal efficiencies under different process variables such as natrium-alkali concentration, reaction temperature, initial pH value, SO₂ concentration, oxidation degree of NOx and additive were investigated. The reaction mechanism for synergistic effect and simultaneous removal of SO₂ and NOx based on the natrium-alkali method were deduced. The removal efficiency of SO₂ was about 100%, but the effect mechanism of denitration efficiency was complex. In this paper, the optimal conditions for simultaneous removal of SO₂ and NOx were determined. The experimental results showed that the simultaneous desulfurization and denitration was possible, and the removal efficiencies could meet the increasingly stringent emissions regulations of IMO.