The accelerated carbonation test was carried out for the ordinary concrete and fly ash concrete. Influences of water-cement ratio, carbonation age and fly ash content on pH value were researched. The results show that carbonation depth, including incomplete carbonized zone, can be effectively reduced by reducing water-cement ratio. So lower water-cement ratio means high performance of resistance of carbonate. The use of fly ash can optimize concrete pore morphology, it’s beneficial for anti-carbonation. However, It disadvantageous to anti-carbonation because of less carbonation material. By taking appropriate mixture of fly ash we can not only enhance the anti-carbonation ability of concrete, but also reduce the use of cement to get well economic benefits.