Abstract This paper proposes a computational mechanical model to evaluate the effect of the angle between loading axis and twin boundary (TB) on the deformation behaviors of nanotwinned materials. In this model, the shear deformation across the TBs and the shear deformation parallel to the TBs were considered. The model correctly predicted the experimentally observed tendency of the influence of twin density on flow strength. Besides, the mechanical behaviors of nanotwinned Cu with different angle were studied. However, as twin density increases, the effect of the angle on the stress–strain relations was weakening. This analysis can offer some useful information for optimizing of strength and ductility.