Abstract: In order to reduce the damage of SO ₃ to the environment and the negative impact on the daily operation of coal-fired power plant units, a simulation study of SO ₃ removal was carried out. First, a numerical model of the whole process reaction of SO ₃ 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 SO ₃ absorption by alkaline absorber were investigated by using sodium carbonate Na ₂CO ₃ solution as alkaline absorber, and the effects of various parameters of alkaline absorber on SO ₃ removal efficiency were also investigated by the model. The results show that the main existence mode of Na ₂CO ₃ in the flue is solid phase, and the flue gas temperature has a small effect on SO ₃ removal efficiency. The removal efficiency of the gun system varies with different arrangements. The removal efficiency is better when the mass concentration of Na ₂CO ₃ is 100 g/L, and the molar ratio is not linearly correlated with the removal efficiency of SO ₃. When the spray particle size is 40 μm to 70 μm and the atomization angle is 60°, the effect is better.