During the search for a highly sensitive sensor of CO2 gas molecule, the adsorption of CO2 gas molecule on both intrinsic and detected graphene sheets was studied by first-principles calculations. We explored that the CO2 gas molecule adsorption on the different elements X (B, N, P, Al) doped mono-vacancy graphene, the results showed that Al-MG was better than B-MG, N-MG and P-MG for the CO2 gas molecule with suitable adsorption strength and apparent band gap. Moreover, Al-MG had a chemical reaction with CO2 gas molecule and came into obvious charge transfers. So sensitivity to CO2 gas molecule made Al-MG was a promising candidate for highly sensitive gas sensor.