Abstract: The exhaust gas of power plant boiler contains trace SO₂ after desulphurization, resulting in poor performance of CO₂ adsorbent. In this paper, according to the composition of flue gas in power plant, CO₂ adsorption performance of K₂CO₃ adsorbent and the effect of SO₂ on CO₂ adsorption are studied by using simulated flue gas under laboratory conditions. Combined with XRD analysis, density functional theory (DFT) is used to study the effect of SO₂ on K₂CO₃ adsorbent and the mechanism of CO₂ adsorption. The results show that under the influence of the active s orbital of S atom in SO₂ molecule, the p orbital of S and O atom are both more active, which degenerated to the valence band maximum of O atom on the surface of K₂CO₃. SO₂ is preferentially adsorbed on O top site of K₂CO₃ surface and pushes CO₂ away from the adsorbent surface, resulting in the adsorbent's active site being free but unable to adsorb CO₂. It shows up in the experiment as follows: when the volume concentration of CO₂ in the simulated flue gas is 10%, SO₂ with a volume concentration of 0.007% in the atmosphere will reduce the adsorption capacity of the adsorbent from 1.65mmol/g to 1.01mmol/g. The adsorption mechanism of CO₂ and H₂O on the surface of K₂CO₃ (001) is proposed. The theoretically calculated reaction activation energy and reaction heat are 40.7kJ/mol and −54.9kJ/mol, respectively.