The strength, non evaporable water content, metakaolin（MK） reaction amount, Ca（OH）2 content, microtopography and pore size distribution of metakaolin cement（MK OPC） hardened slurry with high use level（by mass） of MK were studied. The results indicate that mortar strength increasing rate accelerates as the use level of MK increases within 50% range and the strength of MK OPC mortar is mostly larger than that of plain cement mortar. For MK OPC pastes, as the use level of MK increases, MK reaction amount increases, Ca（OH）2 content decreases, microstructure becomes densification and pore structure refines. MK reaction amount or strengthening factor is in direct proportion to volume increment of pores with d≤10nm.