The surface of K9 glass substrate (with size 90mm×60mm×10mm) was polished by bowl-feed polish. The super smooth surface with roughness less than 1nm and reflective wavefront l /20(p-v) (l =632.8nm ) was got. The high reflective thin film, whose reflectivity is more than 99.5% at wavelength 1054nm for incidence angle 45°, and whose laser induced damage threshold is 26J/cm2 (1054nm, 1ns), was coated on this super smooth surface by electron beam evaporation deposition in the APS1504 coating machine. After alternately coating HfO2 and SiO2 multilayer on the surface, this mirror’s reflective wavefront is l /10(p-v) (l =632.8nm ). The high quality pick-off mirror whose specification is agreement with the designed specification of that type of mirror for the SHEN GUANG Ⅲ was got.