Abstract: Diamond wheel grinding is still the most promising way for high efficiency machining of hard and brittle materials, and it is of great significance to understand the grinding mechanism for high efficiency and ultra precision machining of hard and brittle materials. The static indentation fracture mechanics model and the dynamic cutting approximation model for micro nano cutting are introduced, and the plastic-brittle transition mechanism is explained. The mechanism of brittle removal, plastic domain removal and powdering removal of hard and brittle materials are discussed. The material removal is caused by crack evolution, extrusion micro breakage, phase transformation and dislocation. Plastic domain processing is an important measure to improve the processing damage. The mechanical and thermal coupling field, material crystal orientation and other factors are the key factors affecting the plastic domain removal mechanism.