Laser damage threshold of optical thin film is a critical parameter in measuring laser induced damage. The key to testing damage threshold is judging the injury incident accurately. It has been found that when high-energy laser on the film, there will be sounds generated. In the present paper, acoustic method was applied to determine thin films damage. A brief analysis will be given on feasibility of acoustic method in judging thin films damage. Acoustic acquisition system will be established. In the experiment, we will average laser energy into 10 grades, each grade test 10 points. The sound wave of each point will be record. At the same time, we use image method judge damage of the thin films and record the result. By studying the sound waves of the thin films in different laser energy，it is easy to judge whether the optical films is damaged. The measured result is compared with image method. Both of them have a preferable consistency. The analysis shows that the acoustic method can be used effectively to determine laser-induced damage and it can be used in online inspection conveniently.