Filter is often used to interfere the spectral spectrum into different bands in free space laser communication. This article mainly introduces the research and preparation of a three-band near infrared optical filter. According to the design theory, TiO2 is selected as the material of high refractive index and SiO2 as the low one to realize high transmittance in two bands of 770~860 nm and 1530~1575 nm, and high reflection in the band of 1615~1700 nm. The film stack is designed by film design software, and electron gun and ion-assisted deposition system are used for film preparation. The process flow is optimized through the adjustment of process parameters to get a good thickness uniformity of less than 3% by adjusting the compensation bezel. Although the film is thick, it meets the use requirement as shown by the tests of optical properties, mechanical properties and resistance to the environment. In addition, the quality of the coating surface successfully passes the test of the surface profile instrument, meanwhile, the variation of profile peak-to-valley (P-V) value can meet the design requirements.