Aiming at the rectangular copper bus-bar of 10KV switchgear, lightening optimal designing of the bus-bar is made and its thermal performance is analyzed in this paper. Without changing the surface of the rectangular copper bus-bar, a new lightweight bus-bar is designing by punching on the cross section of rectangular bus-bar in order to save the material and reduce the skin effect. The skin effect and temperature field of new bus-bar are analyzed by ANSYS. The simulation results show that the skin effect of new lightweight bus-bar is significantly reduced, and the simulation results of temperature field are slightly higher than that of the rectangular bus-bar(less than 5o). At the same time, electrify the rectangular bus-bar and the new lightweight bus-bar with same current and do the temperature-rise test. The result shows the temperature rise of new lightweight bus-bar is slightly higher than that of the rectangular bus-bar(less than 5o). Both the simulation and the experimental results show that the thermal performance of new lightweight bus-bar is up to the standard on the basis of saving as much as 15% of the material which can provide the technology support for re-placing the rectangular copper bus-bar in engineering.