Abstract: Infrared lasers at 2 m wavelength have great application value and good prospects in the environmental detection, wind-measuring radar, tissue ablation as well as optoelectronic countermeasure. The films at 2 m wavelength were often prepared by sulphide, arsenide and other soft material which have high refractive index. In order to promote the damage performance of these films, the oxide material was used whose refractive index was relatively lower but the bandgap was wider to prepare the film. The content of OH and the absorption of the film were characterized by using Fourier infrared spectrometer and the weak absorption tester. By optimizing the fabrication process, the multilayers dielectric thin films which satisfy the requirements of the 2 020 nm Tm laser were successfully prepared. The damage morphologies of the films after the laser damage testing were observed by the differential interference microscope, combining with the electric field distribution and the stress in the film, the damage mechanism of the films were analyzed and further optimization method of damage character was put forward.