The thermal damage analysis model of a classical circular cone protuberance on the surface induced by laser is set up. The modulation light field distribution and the temperature field distribution around the defects are calculated by finite-difference method, and the influence rule of the defects on thermal damage threshold is obtained. Results show that the thermal damage threshold increases while incident wavelength of laser increases and the size of defects decreases. In conditions of the same wavelengths, thermal damage occurs first in the defect when there is a defect, while thermal damage occurs in the middle region of the two defects first and it is more likely to make damage when there are multiple defects. For different wavelengths, the laser wavelength of 800 nm is more likely to cause damage in the material than the laser with wavelength of 1064 nm.