The protective AR(anti-reflection) film of infrared wavelength is an important optical film used in army field,it can protect and improve the performance of IR windows or domes.The design and preparation of SiO2 film used for protection and avoiding-reflection in IR wavelength are discussed in this article.In order to resolve the problem of water absorbing in 2900nm,we prepared the film by Ion Beam Assisted Deposition (IBAD) and annealed it after preparation.At last,we get a good SiO2 film deposited on big spherical surface,which has very good optical and mechanical character.