Optical thin film technology has been widely used in almost all optical systems, photoelectric systems and photoelectric instruments. The development of new detectors puts forward filtering requirements for the energy response in the near-infrared 1--3 m band. Starting from the electromagnetic field theory and Maxwell′s equations, the design theory of optical thin films is introduced, and the design method of band-pass filter films is discussed. Using Optilayer software, a band-pass filter film in the near-infrared band is designed with alumina as the base, and the working band is 13--27 m. Considering the matching of coating materials, zinc sulfide and ytterbium fluoride are selected as high and low refractive index materials. The design method combining long wave pass and short wave pass is adopted, and the calculation and optimization of the film system are completed with Optilayer software. The film is coated on both sides of the alumina substrate, and the film system is coated by the preparation process of electron beam evaporation and ion beam-assisted deposition. The prepared samples are tested for transmittance with a spectrophotometer. The test results show that the average transmittance of the sample is greater than 95% in the design waveband of 13--27 m, which meets the requirements of the design of the band-pass filter film.