Herein, a series of imidazole derived task-specific deep eutectic solvents (DESs) based on a protic ionic liquid were synthesized and used for CO2 capture. These DESs exhibited excellent CO2 absorption capacity up to 1.00 mol CO2/mol DES, and the absorption process could be adjusted by the mole ratio of hydrogen-bond acceptor and hydrogen-bond donor. The effect of temperature on the absorption process was also investigated. To deeply investigate the absorption mechanism of these DESs, the corresponding protic ionic liquid was studied and in situ IR analysis was applied for recording the absorption process. With the help of experimental results, NMR spectra analysis, and theoretical calculations, it was found that these DESs captured CO2 via a synergism of cation and anion, and the protonated superbase played a key role in the absorption process. In addition, the DESs studied in this work showed high thermal stability and excellent recyclability.