The structure and electronic properties of the bare and hydrogen-passivated ZnSe/Ge bi-axial nanowires have been calculated by means of the first principle calculation based on density functional theory. Five different types of nanowires with different concentrations all grown along [1 1 1] direction are considered. Band gaps of bare ZnSe/Ge bi-axial nanowires are smaller than those of hydrogen-passivated ZnSe/Ge nanowires at the same doping concentrations. Both the bare and hydrogen-passivated nanowires have lower band gap at a higher Ge components. It is shown detailedly that with increasing of Ge doping concentrations, the main sources of conduction band minimum and valence band maximum of nanowires varied from the p-state of Se and Ge to the p-state of Ge. It is found clearly that there is a transition from the n-type to the p-type characteristics at the doping concentration 0.4211. Whereas, when the Ge composition is increased to 0.8421, the nanowires also have a transition from the p-type to the n-type characteristics. In addition, the structural stability and the cohesive energies of ZnSe/Ge bi-coaxial nanowires are changed obviously with different Ge components. The results offer efficiently guidance to explore their potential applications in photoelectronics.