As the rocks were composed of many minerals, high temperature might lead to the non-consistent deformation among these components. That was the mechanism of thermal damage. In the present paper, the thermal damage of rocks was investigated under a much broader temperature range until minerals phase transition. The experimental techniques of AE and the internal friction were proven to be the most useful tools to reveal the thermal damage. The affection of thermal damage to Kaiser Effect of temperature and the coupled effects of thermal and mechanical damage were also discussed.