Based on the non-cosine film thickness distribution formula of the small area source in electron beam evaporation， the distribution uniformity of optical thin film thickness of the electron beam evaporation spherical fixture system is studied in this paper. At the same time， the mathematical model is established， the shape and position of the correction mask are corrected by MathCAD programming， so as to control the thickness distribution uniformity of the optical thin film. Set the evaporated Ta₂O₅ thin films as an example， the position and shape of the correction mask are optimized， and Ta₂O₅ single-layer thin film with thickness of 600 nm is fabricated. Experimental results show that the actual thickness nonuniformity of the modified baffle optimized by the model is 0.6%， which validates the feasibility and correctness of the model.