Laser induced damage threshold of optical thin films were always a critical parameter. The key technology of testing
damage threshold is determining the incidence of injury accurately. In the present paper, acoustic method is applied to determine thin films damage. Acoustic model of laser-induced thin film has been proposed. The model on the sound waves of thin films damage divides into three stages, which is the thermal expansion stage, the gasification stage and plasma stage. The laser damage optical thin film of sound waves collection system is established. The laser energy is divided into different levels. Acoustic signals under different levels of laser energy are collected. By analyzing and processing of these acoustic signals, we get the sound characteristics of different laser energy; At the same time, damage of films are magnified 100 times, and the sound and thin-film damage is one-on-one mapped. Eventually, we find the acoustic identification basic of damage in thin films. According with the acoustic method of distinguish the film damage, we experiment DLC films. The results are consistent with microscope method. Experiments show that this study of the acoustic method to distinguish the thin films damage is not only feasible, but also reveals the law of thin films damage and acoustic characteristics, and to provide a basis for the acoustic study of thin films damage.