Abstract: The mechanism of laser induced damage on optical films, and the methods to improve the laser-induced damage threshold (LIDT) were reviewed in two respects including theory and experiment. We summarized the existing theory models and their applicable scope, and also discussed the problems about defects from various aspects. The characteristics of different coating technics and after-treatment ways were compared in detail. By gathering the achievements of our own and peer institutions at home and abroad, we generalized the sol-gel technics which could be used to improve the LIDT. We also pointed out the direction of future work considering some newly emerging problems such as contamination in vacuum and the subsurface damage.