Abstract: In order to enhance the transmission of germanium and mechanical feature of the antireflective film, the design and preparation of the high performance infrared wideband antireflective film deposited on germanium substrate by ionbeam assisted deposition are investigated. The selection of film material, the design of film systems and the process of the ionbeam assisted deposition for the film systems are introduced. The measured spectral curves of the antireflection film at 7～11.5μm, deposited by this method, are given. The experimental results show that the peak transmission of the film is more than 99.5％, the average transmission in the designed wavelength range is greater than 97.5％, the film adherency is good， the optical and mechanical properties are stable. These are critical for the application of infrared optical systems.