using fixed concrete slump method,the carbonation resistance of concretes with high-volume fly-ash and ground granulated blast-furnace slag had been studied, and make an approach to size- effect .The results show that the more fly-ash joined in,the more carbonation depth is deeper . The carbonation resistance of concretes with high-volume fly-ash and ggbs is better than only with high-volume fly-ash’s. Size effect on carbonation depth of concretes is also important . Carbonation depth will become deeper as soon as the block size improving .and the early improvement is bigger than the late .The more concretes with high-volume fly-ash and ground granulated blast-furnace slag,the size-effect on carbonation depth of concretes will be more evident.