As common conductive materials, Al wires are used on overhead transmission lines under long-term heating conditions. In this study, the strength degradation behavior and the strength-electrical conductivity relation of the commercially pure Al wires (CPAWs) and the Al-Fe wires (AFWs) annealed at various temperatures were investigated based on the microstructure evolution. The strength degradation rate of the AFW is always higher than that of the CPAW. A linear trade-off relation between strength and electrical conductivity for the annealed Al wires are clarified. The results reveal that the mechanisms behind the trade-off relation between the strength and the electrical conductivity for the annealed CPAWs and the annealed AFWs are the recovery of dislocations and the obvious increase of grain width, which leads to the decrease of strength and the increase of electrical conductivity. The coalescence of precipitate in the AFW leads to the obvious decrease of strength, which results in the higher strength degradation rate for the AFW as compared with that for the CPAW. Consequently, the principle of microstructure design for anti-degradation of Al wire is presented.