To study the relations between the mechanical properties and hydration of cement based materials with high use level of metakaolin (MK), compressive strength of metakaolin cement (MK C) mortars and the relative hydration degree of cement in MK C pastes as well as hydration heat were measured. The relations between non evaporable water amount，compressive strength and hydration heat were also investigated. Results show that compressive strength of MK C mortars can be quantified by the effective contact surface model, in which the dilution effect, the heterogeneous nucleation effect and the pozzolanic reaction are all taken into consideration. The relative hydration degree of cement increases as the use level of MK increases while it firstly increases and then decreases with increasing aging time. The max hydration heat decreases and heat increment increases as the use level of MK increases. The linear relation between accumulated hydration heat and non evaporable water amount at the early ages is different from that at the late ages. And a linear relation exists between accumulated hydration heat and compressive strength at the early ages.