MPB for repair of concrete was prepared by proportionally mixing burned MgO powder(M) with NH 4H 2PO 4 powder(P) and setting modifying admixtures. It has excellent properties such as rapid setting with high strength, high bonding strength to old concrete and so on. The study was focused on the key factors influencing the setting time and strength of MPB, the bonding property of MPB to old concrete and the kinetic feature of the hydration of MPB.