The bare and hydrogen-passivated ZnSe/Si bi-coaxial nanowire heterostructures along [110] direction have been investigated by using the first-principle calculations within density functional theory. The structural stability and electronic property of ZnSe/Si bi-coaxial nanowire heterostructures have been shown by changing the Si components. It is found that the ZnSe/Si nanowires have zero gaps at lower Si components, and then they have the increasing gap at higher Si components. It is seen clearly that there is the transition of band gap form zero to nonzero. With increasing Si components, the ZnSe/Si nanowires can be also achieved as n-type or p-type, in agreement qualitatively with the experimental observations. In addition, the structural stabilities and the cohesive energies of ZnSe/Si bi-coaxial nanowires are changed obviously with the different Si components.