The current-density distribution and giant magnetoimpedance (GMI) properties are theoretically described for the homogenous ferromagnetic wires and composite wi res consisting of an inner conductive core covered by an outer ferromagnetic coa ting. The numerical simulation shows that the current is distributed much close r to the surface for the Cu/FeCoNi composite wires than for FeCoNi homogenous f erromagnetic wires at the same frequency and with the same geometric size and m agnetic structure. When obvious MI effect can be observed, the skin effect has a lready been strong in its ferromagnetic coating. The skin effect is still an imp ortant factor for the GMI effect in composite wires. Above a certain frequency o f about 4MHz, the driving current will flow through the ferromagnetic coating ma inly and the electromagnetic interactions become weaker, the MI behavior in the composite wire becomes similar to that in the homogenous ferromagnetic wire.