• A research on the acquisition of macro-mechanical data of the ITZ in the meso-mechanical calculation of concrete. • The mechanical properties of the ITZ with different mix ratios were measured, the relationship between the bond strength and the microhardness of the ITZ in concrete is established. • A two-parameter linear relationship between the splitting tensile strength of the interface bond and the age and the W/B ratio was established. • The priority order of the calculated value of the interface strength in the numerical analysis of concrete meso-mechanics is proposed. The problem of taking macro-mechanical data of the interface between aggregates and slurry in the calculation of meso-mechanics of concrete was studied in this paper. Through a systematic standard interface test study where the interfacial bond splitting tensile strength method and the interfacial transition zone (ITZ) microhardness method were used, mechanical properties were investigated at macro-scale (bond strength), and followed by ITZ microhardness at meso-scale, moreover the relationships between macro- and meso-mechanical properties were established. The results show that interfacial bond splitting strength of aggregates-slurry gradually increases with increasing hydration age and decreases with increasing water-binder ratio; the ITZ thickness decreases and the ITZ microhardness valley value increases with the extension of curing age. There is a certain correlation between macro-scale mechanical strength of interface and meso-scale mechanics of ITZ. There is a significant linear relationship between the splitting tensile strength of the interface bond and the splitting tensile strength of the cement slurry, so the interface strength can be calculated according to the splitting tensile strength of the slurry substrate. The interfacial bond splitting tensile strength and ITZ microhardness valley have different degrees of correlation. The interfacial bond splitting tensile strength has a particularly significant linear relationship with the microhardness value of the cement paste substrate. Therefore, the calculation value of the interface strength in the numerical analysis of concrete micromechanics should preferably adopt the linear relationship formula with the microhardness of the cement paste substrate.