Abstract: Based on the Cao-feidian northern loop overpass project, the metakaolin-based modifier is prepared by the metakaolin. The effects of the metakaolin-based modifier on the workability, strength and durability of concrete are researched. And the improving mechanism is studied with mercury intrusion porosimetry analysis(MIP). The experiment results indicate that metakaolin-based modifier has obviously improved the compressive strength and penetration resistance of concrete while has no disadvantage effects on concrete’s workability. The pore size distribution of concrete containing metakaolin-based modifier has been optimized to improve the microstructure and enhance the penetration resistance of concrete.