Abstract: Based on the theory of thermal elasticity of spherical symmetry, the laser-induced temperature rise and stress in silica glass or K9 glass, which contain high laser-absorptive platinum inclusion, are calculated from heat conduction and thermal stress equations. Phase change of the inclusion is considered. The optical glass containing inclusion is found to be damaged mainly by either thermal stress or the pressure resulted from boiling of the inclusion. Because of the difference in thermal and mechanical properties between silica glass and K9 glass, the thermal stress in silica glass will not be enough to make it damage before the inclusion vaporizes, and only the pressure due to the inclusion's boiling will serve as the main damage source. While in K9 glass, before the inclusion boils, the