In order to solve the problems of deficient CO2 adsorption sites on Zn/Co zeolitic imidazolate frameworks (ZIFs), Zn/Co ZIFs were thermally treated to promote physical adsorption sites on Zn-N and Co-N bonds and then impregnated with polyethyleneimine (PEI) to promote -NH- and -NH2- chemical adsorption sites. The CO2 adsorption capacity detected on Micromeritics ASAP 2020C increased by 53% to 1.07 mmol/g at 298 K and 1 bar, when Zn/Co ZIF was treated at optimal temperature of 450 degrees C to obtain the maximum Me-N2 unsaturated adsorption sites. This was because of a partial cleavage of coordination bonds between Zn-N, Co-N, C-N and C-N along with dissociation of rationally free methyl groups in the framework ligands, which was supported on density functional theory (DFT) calculation. The Zn/Co ZIF treated at 450 degrees C and then impregnated with 40 wt% PEI exhibited the highest CO2 adsorption capacity of 1.82 mmol/g under the condition of at 298 K and 1 bar, which was 2.6 times higher than that of raw Zn/Co ZIF. In addition, this adsorbent is proved to be regenerable and stable during 9 cycle CO2 adsorption-desorption tests, therefore, PEI-thermally treated Zn/Co ZIF exhibits a very promising application in CO2 capture from flue gas and natural gas.