The ultra-broad band anti-reflection film in 1 300~3 400 nm has been designed and fabricated on acousto-optic crystal.Using electron beam vacuum deposition system and Utilizing technology of co-evaporation of two materials,some obstacles have been overcome,such as obtaining right refractive index from limited materials,eliminating unwished absorption in corresponding band,Absorption is reduced to 0.7%.Through tests,it was found that during the process of co-evaporation,when the material with less stable evaporation rate was evaporated in the first place,and the more stable material wasn′t set to start evaporation until the former material get a steady evaporation rate,the mass ratio of two materials can get tremendous improvements,which is helpful in obtaining the expected index of refraction as well.This method was tested to be feasible through theoretical simulation.The average transmissivity of film prepared in the corresponding band is over 96% ,the film meetenvironment requirements.