N-methyldiethanolamine (MDEA) is a commercial amine with the deficiency of slow CO2 absorption rate. In this study, four amino-functionalized ionic liquids (AFILs), i.e., tetraethylenepentamine dimethylimidazole, pentaethylenehexamine dimethylimidazole ([TMTD][2-MI]), tetraethylenepentamine piperazine, and pentaethylenehexamine piperazine, are synthesized to promote CO2 absorption rate in aqueous MDEA. The result shown that CO2 absorption rate in 20 wt% aqueous MDEA-10 wt% [TMTD][2-MI] was 10.7 times than that of 30 wt% aqueous MDEA, demonstrating the highest CO2 absorption rate intensification in aqueous MDEA reported so far. Furthermore, the mechanism underlying the intensified CO2 absorption rate was elucidated through pH measurement and nuclear magnetic resonance. The comprehensive ability of CO2 absorption and deprotonation of [TMTD][2-MI] was the dominant factor for the excellent CO2 absorption rate intensification.