By utilizing of 2 kW CQ2 laser as a laser source, a Twyman-Green's interferometer, CCD photography technology, and a computer data collection and procession system, the thermal deformations of two types of mirrors have been measured, respectively. The experimental results show that the thermal deformations of the phase-change-cooled mirrors are smaller than those of general silicon mirrors, and that the initial thermal distortions of the mirror surface increase greatly with increasing of laser irradiation time; after about two seconds, the thermal distortions increase slowly. The thermal deformation interferogranis of the mirrors at different times are obtained.