Abstract: In order to study the nanoscratch properties of optical quartz glass, a three-dimensional simulation of the fused silica is carried out based on molecular dynamics method. The model of the fused silica is established by using the approach of melting-quenching and the forming mechanism of the microscopic void in the process of preparation is analyzed by observing the sectional view. During the nanoscratch simulation, the change of the fused silica model and the movement of the atoms around the pore are observed and the cutting force curve is drawn. The influence of the void on the nanoscratch performance is obtained. The results show that the gaps in the fused silica are formed in the cooling process due to the restructuring of the covalent bond and their average diameter is about 0.25 nm. The voids will greatly reduce the existence of material mechanical properties, which causes the fluctuations of the cutting force. When the abrasive sweeps away, the atomic dense area, the thickness of 2 nm, is formed beneath the surface because the voids are compressed. The atomic populated area is the damaged layer due to the loss of strength of the original covalent bonds. Therefore the method of small quantities in high frequency can be applied to increasing the mechanical properties in the ultra-precision machining of quartz glass.