Fly ash from the combustion of coal and silica fume from certain metallurgical operations, are among the industrial by-products that are widely used as mineral admixtures in Portland cement concrete to improve durability and produce high strength and high performance concrete. In addition, due to energy-saving and resource-conservation, both ecological and economical benefit can be achieved by using blended Portland cement. Due to the pozzolanic reaction between calcium hydroxide and fly ash or silica fume, compared with ordinary Portland cement, the carbonation of blended concrete is much more complex. In this paper, based on multi-component concept, a numerical model is built which can predict the carbonation of concrete containing fly ash or silica fume. The proposed model starts with a mix proportion of concrete and considers both Portland cement hydration reaction and pozzolanic reaction. The amount of hydration products which are susceptible to carbonate, such as calcium hydroxide (CH) and calcium silicate hydrate (CSH), as well as porosity can be obtained as associated results of the proposed model during the hydration period. The influence of water-binder ratio and fly ash or silica fume content on carbonation is considered. The predicted results agree well with experimental results.