Abstract: The elastic properties and deformation mechanisms of graphene/Cu composites were studied by using molecular dynamics method, with combination of embedded atom method (EAM), reactive empirical bonding order (REBO) potential and Morse potential together. Young's moduli of the composites with different volume fraction of graphene were obtained as a linear function of the volume friction of graphene, which is consistent with the prediction by Halpin-Tsai model. In addition, the yield stress of the composites can also be improved by the graphene. Based on the comparison of the initial crack propagation in single-crystalline Cu and graphene/Cu composites, it is found that the addition of graphene is beneficial to inhibit crack propagation. Slipping along the graphene surface explains the deformation mechanism of the composites, and the results indicate graphene can dramatically improve the plastic deformation capability of the composites.