Laser shock processing utilizes mechanical effect with ultrahigh strain rate to generate deeper residual compressive stress and grain refinement layer, which improves mechanical properties, such as fatigue resistance, wear resistance and corrosion resistance. To date, it is very difficult to present dynamic microstructure evolution at ultra- short time (several ten nanoseconds) during the plastic deformation at ultrahigh strain rate using experimental method. At temperature of 300 K, a molecular dynamics of polycrystalline Cu with a loading duration of 15 ns at a strain rate of 2×107 s-1 is conducted to describe the microstructure evolution process with the LAMMPS soft. Under the mechanical effect of laser shock wave with a ultra-high strain rate, deformation twinning is the important microstructure of grain refinement of the alloys with medium stacking fault energy.