Abstract: Single point diamond turning can make the surface of the aluminum alloy have good quality and precision, but the left turning grains cause scattering phenomenon that affects the optical effect which hardly meets the requirement of high quality optical system. Direct optical polishing on the surface of the aluminum alloy can remove the turning grains which are caused on the surface and can improve the optical performance of reflecting surface. This experiment adopted the new polishing disk and polishing solution to conduct the polishing test over the surface of the aluminum alloy by single point diamond turning. The result shows that we can remove the periodic turning blade lines remained on the surface of the aluminum alloy through reasonable control of the technological parameter, and by which there is no new superficial scratch, so that we can get better optical superficial quality of the aluminum mirror. The roughness on the surface of the aluminum mirror is 2.6 nm.