Fluorogallate glass is an infrared window material with good performance. In order to improve the window observation, detection and protection performance, three-band(0.4--0.9 m, 1.064 m and 3.7--4.8 m)composite anti-reflection protective films are designed and prepared on the fluorogallate substrate. According to the requirements of optical performance and environmental stability, the thin-film materials are selected and the membrane system is designed, and then the multilayer film is prepared by the electron beam evaporation method. The measurement results show that the water absorption peak at 2.9 m lowers the transmittance in the mid-infrared waveband. The film density is improved by improving the process and post-treatment and other ways, and the water absorption of the film layer is effectively suppressed. The environmental stability of the coated components is verified by the boiling-water immersion method. The results show that the thin-film samples processed by ion-assisted deposition and annealing have better optical properties and environmental adaptability.