This paper focuses on researching on the design method of correction masks utilizing for the mirror coating and aims to improve the film thickness uniformity based on ZZS1800-1/G vacuum coating machine, which equipped in Nanshan Station of Xinjiang Astronomical Observatory. By establishing the film thickness distribution model and using high precision numerical calculation, we studied the effects of structural parameters corresponding to ZZS1800-1/G vacuum coating machine and geometry structural parameters corresponding to different mirrors on film thickness uniformity, and analyzed the relevance between the shape of correction mask and the position of evaporate sources, parameters of the mirror, and display the simulation and numerical validation results of correction mask. Results showed that the distance between the evaporation source and the origin was the most obvious influence on the thickness uniformity of the mirror film with larger radius in the rotary planetary fixture system. When the distance was within 600 mm, and the mirror radius was less than 100 mm, and the uniformity of film thickness was less than 1.7%; when the mirror radius was 600 mm, the best uniformity of film thickness was 23%; and the theoretical value of the uniformity was 0.035% after adding correction mask, which shows the necessity of adding correction mask. The deformation of the correction mask needs to be within 2.2% for the purpose of keeping the uniformity less than 1% when the mirror radius was 600 mm. Correction mask can effectively improve the uniformity for ZZS1800-1/G vacuum coating machine, the simulation model proposed in this paper provides theoretical reference for the design of the masks.