Abstract: The effects of running conditions such as operating temperature, heat exchange quality between bars and ambient, and current capacity on the conductivity of copper cladding aluminum (CCA) flat bars were analyzed by a numerical analysis method. The results show that the rate of power loss increasing is smaller than that of direct current resistance increasing due to operating temperature rising. When the sectional configuration of cladding layers is the same, the mean current density which CCA fiat bars can carry decreases with the sectional area increasing. CCA flat bars can replace copper fiat bars when their direct current resistance is the same. This saves copper resource and reduces cost, at the same time the carrying capacity of bars increases. The power loss and operating temperature of CCA flat bars are lower than those of copper fiat bars.