Abstract: The determination method of laser damage of thin film and the evaluation method of damage threshold are indispensable for enhancing anti-laser ability of infrared system observation window and its operating performance. The damage characteristics and mechanism of film by pulse laser induced damage were researched. The experiments used by YAG pulsed laser for TiO2 thin film were offered for 1-on-1 way of laser induced. By using the two images taken from charge coupled device (CCD) before and after laser illumination, the matching of the damaged image and the undamaged image was realized, and the difference image measure algorithm was established. The experiments conclude that the different energy measures of TiO2 thin film samples can identify the damage situation:the measure value M0.1, no damage; 0.1M 0.2, mild injuries;0.2M0.5, moderate damage; M0.5, serious injuries. The roughness of thin film samples irradiated by the laser with the energy density of 0.5 J/cm2 increases obviously. The results show that the method of image matching test before and after laser irradiation can realize discrimination of laser-induced film damage.