Cube concer retro-reflector is an optical element with high reflectivity, widely used to improve safety in low light level environments. High-precision and surface finish die cores are used to mass produce high-quality retro-reflectors. There are periodic micro-morphologies on the die core surface machined by diamond fly-cutting, which weaken the reflection characteristics of optical elements. The finite element method theoretically revealed the relationship between optical defects and surface topography, and the fly-cutting experiment was carried out to verify the analysis. At the same time, an efficient machining method to eliminate the diffraction phenomenon is proposed. According to the machining results, the error source of this method is analyzed and calibrated. This research provides a new idea for obtaining the optical plane of retro-reflector with high efficiency and accuracy.