CO₂ capture plays an important role to mitigate CO₂ emissions. Deep eutectic solvents (DESs) as promising absorbents for CO₂ separation have raised lots of attention. As a new class of ionic liquids (ILs), DESs maintain most of the favorite properties of ILs but avoid their economic and environmental problems. However, the viscosity of the synthesized DESs is relatively high, resulting in slow mass transfer rate (or slow sorption kinetics) and then may lead to a large equipment-size. The CO₂ solubility in the DESs still needs to be improved. In our work, 35 DESs were prepared and screened in terms of their CO₂ solubility and viscosity. Among them, 15 DESs with high CO₂ solubility and low viscosity compared to the conventional ILs were chosen as the promising candidates. In addition, the effect of water as a co-solvent for the glycerol-based DES with relatively high viscosity was investigated, and two other DESs that demonstrated relatively high sorption capacity and low viscosity were chosen for functionalization to further improve their CO₂ sorption capacity. The results showed that the viscosity decreased drastically from 716 to 20 mPa·s, while the CO₂ solubility increased from 0.26 to 0.33 mol/kg DES by the addition of a small amount of water into the glycerol-based DES (BTMA/GLY (1:2)). The further increase of the amount of H₂O decreased the CO₂ solubility due to the low CO₂ solubility in H₂O. In addition, after functionalization of TPAC/ EA(1:4), the CO₂ solubility increased from 1.4 to 3.2 mol/kg DES, which showed a better performance compared with the common ILs.