The bubble on mitigated damage site is the major factor leading to th e re-initiation damage of mitigated site induced by laser irradiation.The types and characteristics of bubble are firstly investigated in this paper by evaporative and non-evaporative methods during the repairing process.The experimental results i ndi cate that no matter which type of method, the bubble can be basically divided into two types,spherical and irregular elli psoid-shaped bubbles.It is found that the type of bubble seriously depends on the shape and the size of crack around the damage site.The damage testing results indicate that the damage threshold of mitigated sites will decrease exponentially with the in creasing of bubble number.The controlling and elimination methods of bubbles during the repairing process are discussed,a nd the optimized treatment parameters are presented at last.