Thin film filters were prepared by evaporation method, and the samples were soaked in DI-water for 10 days and 30 days respectively. By using spectral photometer, dark field microscope, and scanning electron microscope, stability of induced transmission filters in moisture environment was studied. The experiment results show that the layers delaminations of filters often initiate and expand from microdefect sites in the films in moisture environment. Microdefect in thin films is one of the most important influence factors on the filters environment stability, and impurity and pinhole are two main sorts of defects in thin film filters. EDS energy spectra analysis indicates that component of the impurity is Al_2O_3 coating material itself. So it is reasonable to deduce that the sputtering in film position process may be the original reasons for the defects generation, and sputtering restraining is a useful method to improve the stability of the optical filters. At last, the diffusion theory was used to analysis the ......