Ionic liquids (ILs) as a new class of gas dehydration solvents, in combination with the traditional triethylene glycol (TEG) solvent, were first proposed for carbon dioxide (CO2) dehydration. Among 210 preliminary ILs, the hydrophilic [BMIM](+) [BF4](-) was selected based on the COSMO-RS model-involved IL screening methodology. The solubilities of CO2 in pure TEG, pure [BMIM](+)[BF4](-), binary mixture of TEG + [BMIM](+)[BF4](-), and ternary mixture of TEG + [BMIM](+)[BF4](-) + H2O were measured experimentally. Two new binary interaction parameters were introduced by correlating a series of experimental data with the UNIFAC-Lei model. The COSMO-RS model along with the reduced density gradient method was applied to interpret the nature of interaction between molecules. The CO2 dehydration experiment was conducted in a laboratory-scale absorption tower. The process simulation indicates that, in comparison with pure TEG, the use of IL purely or mixed with TEG improves both separation performance and process energy penalty.