Abstract: A numerical simulation was conducted using SPH for the constitutive behavior during metal cutting for complex materials, and the basic rules in metal cutting process were analyzed. The simulation results showed that the cutting process is actually a plastic deformation process in which the material layer being cut forms shearing slip because of the extrusion by cutting tool. The yield strength of the agglomerated material due to extrusion increases in the vicinity of cutting edge. It makes contact stress increase, and eventually results in microcrack on workpiece surface. The cutting force increases gradually, and then varies steadily in a certain range in the cutting process. After the formation of chip, the maximum contact stress on rake fluctuates at a certain distance to the cutting edge, where the cutting-tool is heavily worn.