The increasing demand for designing and manufacturing micro parts with high quality comes from the high speed development of micro electromechanical systems (MEMS) and nano electromechanical systems (NEMS) in recent years. Nanometric cutting as an important machining way of micro parts has become a hot spot in machining field. Some main issues in nanometric cutting such as chip formation, machined surface quantity and diamond tool wear etc., have been investigated by molecular dynamics. Previous researchers have pointed out that the generation and evolution of defects are mainly responsible for causing plastic deformation of machined workpiece in nanometric cutting of plastic materials and a high compressive stress remaining in shear zone is considered beneficial to ductile–mode machining of brittle materials. Up to now, however, the influence of cutting thickness on defect behaviors and stress distribution in a workpiece and the relationship between them for single crystal materials are still unclear. In the present study, molecular dynamics simulations of nanometric cutting of single crystal Cu were performed. The simulation results show that stacking fault and partial dislocation are two main types of the defects in workpieces. A high surface stress at the atomc scale was observed in workpieces and there exist the compressive stress in shear zones and tensile stresses in the machined surfaces. It is found that the stress–distance curves of workpieces present a clear periodicity corresponding to the generation and evolution of dislocations in them. At he beginning of cutting (a small cutting thickness), no apparent stacking faults inside workpieces have been found, but with the increase of cutting thickness, the defects on surfaces and subsurfaces increase significantly and the thicker the cutting thickness, the smaller the corresponding stress components.