Ionic liquids are widely used as potential absorbents in gas separation technology,especially for acid gas capture from flue gas streams and natural gas.[1,2] In this paper,the chemisorptions of CO2 by a series of ionic liquids with functionalized anions are studied.The density functional theory study on the absorption of CO2 by the ionic liquids is taken firstly and the mechanisms of how the CO 2 interacts with the ionic liquids are analyzed.The cations and anions connected with each other by forming hydrogen bonds.The ionic liquids absorb the CO2 by a nucleophilic addition of the anion to CO2 and forming a C-O single bond.All the analyses from the molecular orbital,natural charge,and density of state prove the interaction between the ionic liquids and CO2 molecule are strong chemisorptions.Then the ionic liquids which show better absorption capacity in the quantum calculation are chosen for further experimental research.The solubility of the CO2 in these ionic liquids is studied by different factors such as temperature,pressure,and CO2 concentration.The microscopic mechanisms of absorption are revealed by combining the results of the experiments and the quantum calculations.The rules of the relationship between the CO2 solubility and the micro-structure of the ionic liquids are revealed.