To meet the technical requirements of the 278-nm laser system, a separation film for frequency doubling is developed to separate the double frequency laser and quadruple frequency laser. Combined with the laser damage thermal effect and intrinsic absorption of the materials, Hafnium and UV-SiO₂ are chosen as film materials and the well-cleaned JGS1 quartz glass is used as the substrate. According to the thin film theory and laser damage field effect mechanism, the periodicity variation in electric field intensity distribution of the film is studied and design of the frequency separation film is completed by Macleod software. The chemical composition, optical properties, and surface roughness of the film are analyzed using X-ray photoelectron spectroscopy, spectrophotometer, and ZYGO interferometer, respectively. In comparison with experimental results, the deposition technology of the film is optimized to improve the film growth process and reduce external absorption. Experimental results show that the transmittance of films is 98.82% at 278 nm and reflectance is 99.80% at 556 nm when the incident angle is 45°. In the wide incident angle range of 40°-50°, spectral performance can meet the requirements of the target. The laser-induced damage threshold is 12.53 J/cm ², which meets the needs of use.