Numerical simulations have been carried out to determine the mechanical property of single crystal copper nanowire subjected to tension using the molecular dynamics method. The mechanism of deformation, strength and fracture are elucidated based on these numerical simulations. No strengthening is found after yielding of the single crystal nanowire. The simulation results show that the strength of copper nanowire is far greater than that of realistic polycrystalline bulk copper. By decreasing the size of the nanowire's cross-section, which leads to an increase of the ratio of surface atoms, the yield stress is increased. The strain rate has an influence on strength, and mechanism of deformation and fracture. When the strain rate is comparatively low, plastic deformation arises from dislocation slips and twins. However, when the strain rate is sufficiently high, amorphization is a dominant factor of plastic deformation and super-plasticity is found. The fracture process is demonstrated using the atomic images.