Abstract: The deformation mechanism and mechanical properties of nanocrystalline copper with a bimodal structure (grain size obeying bimodal distribution in statistics) were systematically investigated by combination of molecular dynamics simulation, visco-plastic constitutive model and nanoindentation test verification. The results show that during the plastic deformation, dislocations were first nucleated and expanded in the fine grain zone of the nanocrystalline copper, and the directions were parallel to each other; while the dislocation slip directions in the coarse grain zone crossed each other, and the larger the size of coarse grains, the more likely dislocation entanglement and cross-slip occurred. The flow stresses of the nanocrystalline copper with a bimodal structure increased with increasing coarse grain size, and the hardness decreased with increasing volume fraction of coarse grains. The stress variation law calculated by the visco-plastic constitutive equation was consistent with that by the empirical formula and molecular dynamics simulation, and the relative error between the flow stresses calculated by the constitutive equation and the empirical formula was less than 5%.