For improving the durability of prefabricated components made of steam-cured concrete, the effect of individual and compound mineral admixture on the capillary absorption coefficient and resistance of chloride ion penetration were analyzed, and its mechanism was studied with concrete porosity tested by the evaporable water content method. Results indicated that the transportation properties of steam-cured concrete was greatly improved by mineral admixture at low water-binder ratio. The improvement effect of mineral admixture on the transportation properties of steam-cured concrete from the greatest to the least is silica fume (SF), metakaolin (MK), ground slag (GS) and fly ash (FA) at the stage of demould and 28-day. The effect of MK was equivalent to that of SF at 90-day stage, and these two mineral admixtures were superior to GS and FA. The concrete pore structure had close relationship with transportation performance. The decrease of porosity and the refinement of pore size contributed mostly to the improvement of the transportation properties of steam-cured concrete.