In order to obtain the micro mechanical properties of interfacial transition zone(ITZ) of steam-cured concrete with metakaolin(MK), the micro-hardness of the interface area of steamed concrete with different MK content was tested, probabilistic statistical methods were used to process ITZ micro-hardness data of steam-cured concrete incorporating MK, and its action mechanism was clarified by thermogravimetric analysis and scanning electron microscope. Results indicate that micro-hardness data of the ITZ take on obvious discrete distribution characteristics, and do not meet the normal distribution, and more in line with the 3-Parameter Lognormal Logistic distribution. Using 3-Parameter Lognormal Logistic distribution makes the discreteness of the ITZ micro-hardness curve reduced and the characterization of ITZ strength is more accurate. Metakaolin increase concrete ITZ micro-hardness, and with the increase of curing age, the micro-hardness value of concrete ITZ increase and the ITZ width decrease. Under steam curing conditions, MK occurs a secondary hydration reaction with more consumption of Ca(OH)2, and Ca(OH)2 crystals . More C-S-H gel are produced and the ITZ of steam-cured concrete is densified.