Using micro-wave heating method, the previous disadvantages of heating slowly and non-uniform are broken through. And plain concrete high temperature loading experiment system is composed of the method and material experiment machine. Many experiments of self-made concrete are carried out from room temperature to 600°C by this system. The strength and critical strain of concrete with temperature are obtained, and through analysis of the compressive stress-strain curves under different temperature, the constitutive relationship is established. The result shows that this constitutive relationship is greatly agrees with experiment. Meanwhile, the phenomenon is analyzed and explained in the progress of experiment.