The method of grinding a high precision or hardened gear using high quality 9' grinding wheel is called gear grinding. It is an effective processing method for obtaining high production efficiency and ideal processing quality in various processing gear methods. Gear grinding has been widely used in the precision machining of idle speed, precision gears, gears of certain indexing mechanisms and gears of China abrasive tools for metal. The way of gear grinding can be divided into two methods: copying method and forming method. The profiling method uses a dressing wheel to directly grind the teeth. The forming method is based on the principle of gear meshing, the relative movement of the high quality 9' grinding wheel and the workpiece. According to different types of gear grinding machine structure and grinding requirements, it can be divided into double cone grinding wheel type, double disc type grinding wheel type, large plane. The high quality 9' grinding wheel type and worm type (grinding small modulus gear). Due to the structure of the gear grinding machine of various grinding methods, the operation mode, the grinding speed, and the feed amount limitation, there is less room for a selection of China abrasive tools for metal characteristics of the gear grinding. If the hardness of the grinding wheel is low, the high quality 9' grinding wheel of the grinding process will wear a lot, and the correct geometry will not be guaranteed, which will cause machining error of the tooth shape. If the hardness is too high, the gears of high-strength alloy steel materials with high hardness (martensite structure) after hardening treatment are prone to cracks during grinding, burned and processed metamorphic layers, and reduce the processing of gears. The quality, and therefore the selection of the high quality 9' grinding wheel of the gear grinding should pay attention to both hardness and organization.