To establish the scientific principles and technical frameworks of the ultra-precision grinding technology, the research work was performed on the processing principles and methods of the ultra-precision gear-grinding to develop the ultra-precision master gears with class 1(ISO 1328-1: 1995). Firstly, according to the optimal forming of an involute and the easy refinement and high structural rigidity of the machine, the gear grinder with flat-faced wheel Y7125 was chosen as the object machine tool. Then the ultra-precision gear-grinding processing was discussed and studied from the aspects of gear blank processing and datum renovation, optimal adjustment of grinder parameters and scientific gear-grinding operation. Finally, the medium module (m2 and m4) ultra-precision master gears with class 1 were developed by a scientific gear-grinding experiment. The research on ultra-precision gear-grinding processing plays a guiding role in the overall improvement of gear manufacturing technology in China.