In order to improve the surface quality and diffraction efficiency of CaF₂ diffraction optical element (DOE) processed by single point diamond turning, a mathematical model is proposed to reveal the effect of surface roughness error and surface profile error on diffraction efficiency based on Beckman scalar scattering theory and effective area method first. Then, the turning model of CaF₂ DOE is optimized combining with the turning characteristics of CaF₂ and the structural characteristics of DOE. At the same time, the optimal turning positions and tool radii of half-round tool under different process conditions are given, which realizes the control of the surface roughness of CaF₂ DOE. Finally, the high surface quality CaF₂ DOE with a surface roughness of 3.4 nm and a shadow region width of 28.7 μm is obtained with the guidance of the optimized model, which verifies the reliability of the proposed optimized turning model. The proposed optimized turning model has great significance for improving the imaging quality of the refraction-diffraction hybrid optical system containing CaF₂ DOE.