Little research was carried out to study the effect of water vapor with different contents on the CO2 adsorption performance during extending cycles in both carbonation and decarbonation stages. This study described the CO2 adsorption performance of Ca-Al mixed oxides under different water vapor concentrations. The results revealed that the reactivity and durability of both fresh and spent sorbents were remarkably enhanced by adding water vapor. The initial CO2 carbonation capacity increased from 56 wt% without water to 70.7 wt% with 1.6% water vapor at the adsorption temperature of 600 degrees C. The stability of Ca-Al mixed oxides was also investigated during 220 cycles with 1% steam vapor. The CO2 adsorption capacity retained 55.6 wt% after 220 cycles, indicating an excellent long-term durability. The excellent CO2 adsorption capacity and stability of the mixed oxides in the existence of water vapor may be attributed to the following reasons: water vapor facilitated CO2 diffusion in the CaCO3 product layer during the carbonation stage as well as the decomposition rate of CaCO3 during the calcination stage; water vapor facilated the formation of the loose porous structure, which was favorable for the subsequent carbonation of CaO.