Abstract: In order to reduce the damage of SO₃ to the environment and the negative impact on the daily operation of coal-fired power plant units, a simulation study of SO₃ removal was carried out. First, a numerical model of the whole process reaction of SO₃ absorption by alkaline absorber in multiphase flow was established using the tail flue of a coal-fired unit as a simulation object. Then the basic characteristics of SO₃ absorption by alkaline absorber were investigated by using sodium carbonate Na₂CO₃ solution as alkaline absorber, and the effects of various parameters of alkaline absorber on SO₃ removal efficiency were also investigated by the model. The results show that the main existence mode of Na₂CO₃ in the flue is solid phase, and the flue gas temperature has a small effect on SO₃ removal efficiency. The removal efficiency of the gun system varies with different arrangements. The removal efficiency is better when the mass concentration of Na₂CO₃ is 100 g/L, and the molar ratio is not linearly correlated with the removal efficiency of SO₃. When the spray particle size is 40 μm to 70 μm and the atomization angle is 60°, the effect is better.