Based on the film thickness theory model of planetary fixture, the film thickness distributions of hemispherical lens surface are studied theoretically. The film thickness formulas of typical points on the hemispherical surface are calculated, and then the thickness distributions in different situations are calculated by substitution method. The results show that the thickness non-uniformity in central region (within a 90-degreee angle) of the hemispherical surface could be controlled at about 10%, and that in edge region (over a 90-degreee angle) could be as high as 90%. Changing the location of evaporation source has no effect on improving the thickness non-uniformity of hemispherical surface. However, changing the evaporation source can improve the thickness non-uniformity. This research has certain theoretical guiding significance for the analysis and improvement of film thickness uniformity of hemispherical lens coating.