Single-point diamond cutting is the best method to machine the KDP crystal. On the basis of independent study and development, the key technologies of ultra-precision gas hydrostatic spindle and guideway design and manufacturing, constant velocity direct drive technology of high precision spindle and worktable are solved and DFC-600A ultra-precision single-point diamond fly cutting machine tool is developed successfully by studying the single-point diamond cutting mechanism thoroughly. The process experiment results demonstrate that this machine tool can realize the ultra-precision machining of large-scale optical components, such as KDP crystal, aluminum alloy and polycarbonate.