As an ion beam emitting device, ion source is often used in the preparation of optical films. However, the ion beam contains ions with various energy, which seriously affects the microstructure and properties of optical films. In view of the disadvantage that the output energy spectrum of ion sources at home and abroad is too wide, based on the electromagnetic field theory, the ion motion trajectories of each energy level are simulated and analyzed, and an ion energy filter is designed. The results show that the filter can effectively remove the ions with too high and too low energy, and the screening rate deviates from the central ion energy by negative 100eV, It has reached 82.24%, and has a good application prospect in the field of optical film preparation.