The carbonation resistance of high fluidity(about 180 mm) concrete containing fly ash, ground granulated blast furnace slag and superplasticiser was studied. Experimental parameters, such as substituting content for cement(maximum:80%) and proportion of fly ash to slag were varied. Relation of carbonation depth of concrete to time is described by the equation d=at b , in which b ranges mostly from 0.3 to 0.4. Both fly ash and slag are used to increase the total substituting content of cement. For example, from the point of carbonation resistance, concrete designed for 50 years service life allowes addition of fly ash by 40% if all other engineering requirements are satisfied. When both fly ash and slag are added, the total addition rises to 60%,70% and 80%, in which fly ash occupies 40%,30% and 15%, respectively.