Abstract: The load-crack mouth opening displacement (P-CMOD) curves at some typical ages were obtained for three kinds of concretes, and their compressive strengthes at 28 days are around 30MPa, 50MPa and 80MPa respectively, through a three-points bending test. From the P-CMOD curves, the development of cracking strength, tensile strength and flexural strength of the three concretes with an age was obtained. The effects of the curing condition on above mechanical parameters were investigated. Taking account of the effects of interior RH on cement hydration, the cement hydration under a drying condition was modified and a cement-hydration-degree based model for cracking strength, tensile strength and flexural strength predictions was developed.