Abstract: High silicon aluminum alloy (Al-30wt%Si) has good physical and chemical properties, but it is difficult to process the material because of the existence of silicon particles in the internal reinforcement phase. Ultrasonic vibration-assisted cutting has obvious advantages in improving the machinability of high-silicon aluminum alloy materials, but the microscopic mechanism in the machining process still needs to be studied. The conventional cutting and ultrasonic vibration-assisted cutting of high-silicon aluminum alloy were simulated by molecular dynamics method, and the surface formation process and subsurface damage mechanism were explored by analyzing cutting force, temperature, stress distribution, phase transformation and dislocation. Through the analysis of diamond structure identification, tool deformation state and radial distribution function, tool wear was studied. Cutting speed is closely related to cutting force, temperature and crystal phase transformation. Ultrasonic vibration-assisted cutting can effectively reduce cutting force and stress, but its temperature and crystal phase transformation ratio will increase. Cutting depth significantly affects cutting force, surface morphology and subsurface damage. Ultrasonic vibration-assisted cutting changes stress and dislocation distribution, which is of positive significance for improving surface quality and reducing subsurface damage. This study expounds the relationship between machining parameters and mechanical properties during nano-cutting, and analyzes the micro-damage mechanism of cutting high-silicon aluminum alloy, thus providing a micro-level reference for the research on cutting mechanism of ultra-precision cutting difficult-to-machine materials.