Using TEM, SEM and XRD, the surface microstructures of nanocomposite ceramics prepared by heterocoagulation was studied in two-dimensional ultraprecision grinding with ultrasonic assistance. This research was focused on the structure of ground surface degenerating layer, surface generation mechanism and characteristics of nanocomposite ceramic parts. The experimental results showed that the microscopic deformation mechanism of the ordinary Al2O3 parts was grain- boundary twinning and grain-boundary sliding while microscopic deformation mechanism of nanophase ceramic parts was the inner crystal dislocation of strengthened phase with intragranular structure. And its deformation coordination mechanisms were the grain-boundary sliding and coordination deformation of intercrystalline second-phase. The observation on the fracture surfaces of nanocomposite materials with different microscopic structures by TEM and SEM showed that ZrO2 particles had an important effect on the generation and expansion of crack in ceramic parts. The introduction of ZrO2 particles strengthened the interface intensity of grain boundary. If there were rich ZrO2 particles on the grain boundary, the cracks generated during the grinding process would be prevented. Smooth and plastic deformation processing surface was obtained. It was proved further that the nanophase materials behaved transcrystalline fracture due to the nano particles, dispersed in the grain boundary and prevented the expansion of crack. This material’s fracture behavior made favorable surface possible. In the precise grinding of nano materials, the plastic removal mechanism dominated the process. The dislocated depth of the nanocomposite ceramics after grinding was bigger than that of common ceramics, which meant that dislocation increased.