Abstract: A new test rig was developed by modifying the clamps and the control system of conventional pin-on-disc tester. The friction and wear characteristics of aluminum-stainless steel composite conductor rail and collector shoe used in metro power supply were investigated on the rig with an electrical current applied across the sliding interface. The morphologies of worn surfaces were observed and analyzed by means of laser confocal scanning microscope and energy dispersive x-ray spectroscopy. Wear mechanisms with electric current were analyzed and discussed based on electric contact theory. Experiment results show that a threshold value of normal stress exists in friction and wear with the variation of electric current. If normal stress is larger than the threshold value, friction coefficients increase with the increasing of electric current, and current enhances mechanical wear. If normal stress is smaller than the threshold induces electric arc erosion. value, friction coefficients decrease with the increasing of electric current, and current Wear mechanisms of the part with current are dominated by adhesive and abrasive wear, but the material volume loss caused by electric arc erosion is much larger than it caused by mechanical wear. For a certain velocity, the threshold value of normal stress is an optimum normal stress, which makes not only electrical power supply stable but also mechanical wear lower and railway running cost saved.