The propagation of shockwave in nanocrystalline copper has been studied by means of molecular dynamics simulation. The samples are prepared by Voronoi method and crystalline orientations of each grain are limited by three conditions. The result shows for the first time that nanocrystalline copper shows the phenomenon of multi-yield under shock loading, and the shockwave has a multi-wave structure. The profiles of shock-front suggest grain boundary sliding and dislocation emmision in sequence. The shock-front consists of an elastically deforming area, a plastically deforming area dominated by grain boundary sliding and a plastically deforming area dominated by dislocation movement. There are irregularities on both elastic wave and plastic wave, and the former is obvious than the latter.