The gas permeability coefficient and CO2 diffusion coefficient of concrete under load were investigated and the relationship between the aforementioned two parameters was established. Further, on the basis of the carbonation model based on Ficks first law of diffusion, a new prediction model of concrete carbonation depth using the gas permeability coefficient as the characteristic parameter was proposed and verified, and it was named CDep GPL. The results show good consistency between the calculated values and the tested ones. The CDep GPL model can be used to predict the carbonation depth of concrete under load.