The method of fitting damage probability curves of laser-induced damage is introduced to investigate the laser-conditioning mechanism of ZrO2/SiO2 high re°ection (HR) films. The laser-induced damage thresholds (LIDTs) of the sample are tested before and after the laser-conditioning scanning process. The parameters of the defects are obtained through the fitting process of the damage probability curve. It can be concluded that the roles of laser conditioning include two aspects: removing defects with lower threshold and producing new defects with higher threshold. The effect of laser conditioning is dependent on the competition of these two aspects.