As an important parameter of high-precision optical films, thickness uniformity plays a vital role in their performance. Large-size high-precision reflective films have especially high requirements for thickness uniformity. In this paper, the efficiency and accuracy of the uniformity correction of thin films are greatly improved by studying the emission characteristics and film thickness distribution of the evaporation source, combining Mathcad software to establish precise mathematical and physical models, writing automatic programs, and simulating the correcting mask shape. Through this method, an aspherical deep ultraviolet reflector with a diameter of 320 mm is prepared on public autobiographical planetary evaporation deposition equipment. The average reflectance at 240-300 nm ultraviolet waveband is greater than 97.5%, and the uniformity is better than 0.5%. This research provides a theoretical basis and technical support for the uniformity correction of large aperture aspheric films.