Ultra-precision large-sized milling technology is the machining technology of parts with high precision and high surface quality. The flatness of the processed parts in general milling is technically required to be more than 5 μm. The surface roughness (Ra) of the processed parts is technically required to be more than 5 nm. Advanced single-point diamond turning technology (SPDT) has been widely used internationally for machining flat parts. This technology refers to the use of natural single-crystal diamonds as a tool for the cutting, milling, and processing of optical surfaces under computer control. It is a new technology that was developed in the early 1980s. After more than 20 years of development, it has been widely used in processing a variety of high-precision optical components.