According to the technical requirements of the laser and far infrared common-window imaging system, a wavelength separation coating was developed, which aimed to separate the laser and far infrared light through a common window, that is, 1 064 nm laser reflected, 8~14 μm far infrared light transmitted. By analyzing the microstructure of the films, the refractive index changes of the films before and after moisture absorption were studied. The structure of the films was optimized by combining the optical film theory. On the basis of studying the stress of the film, the film thickness was optimized and the film firmness was improved. The average transmittance of the wavelength separation coating in the bands of 8~12 μm、 12~14 μm are 97.1%, 90.1% and the reflectivity of 1 064 nm is 99.71%. The separation coating can meet the technical requirements of the imaging system for a long time in various military outdoor environments.