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We performed molecular dynamics simulations of nano-indentation on Cu/Ni coherent multilayer films with different individual layer thickness to investigate the Strengthening and softening mechanisms.We found that the two hard models and one softening model,correspond to three possible types of dislocation–twin-boundary interaction,obtained through pure nano-twinned metals can be applied to Cu/Ni multilayer film with nano-twinned interface,however,cannot be applied to that with coherent interface.Even so,there is still a critical range of individual layer thickness,in which hardness of the multilayer films can maximize or otherwise it descends.These Hall-Petch and inverse Hall-Petch like relations should be attributed to the competition between strengthening and softening mechanisms.Moreover,we also conducted a systematic analysis of strengthening and softening mechanisms with microstructures at characteristic depths.