This paper reports an innovative structure of laser reflecting mirror cooled by phase-change. Cooling channels are built up in reflecting mirror of positive-branch virtually-confocal unstable resonator, stuffed solid-liquid phase-change materials for maintaining mirror's temperature at a comparatively constant point. This mirror, whose structure is simplistic, could be united with crystal output window, neglecting 45° plate scraper for output coupling, and then high quality output beam is available.