Abstract: The tribological behavior of PAO-lubricated DLC contacts under DC electric field was investigated on a designed tribo-meter with a ball-on-disk configuration, and the effects of sliding speed, applied voltage and electric current were studied. The results show that the influence of applied DC electric field on the friction and wear of DLC strongly depended the sliding speed, which could be ascribed to the different electrical damage and corresponding changes in the microstructure of DLC coating under different lubrication regime. According to the lubrication regime of DLC contacts and applied voltage, the electrical damage of DLC coating could be liner bulges or ablated pits. It is found that the liner bulges were caused by the high joule heat generated at the sliding interface with electric current, while the ablated pits were produced by the arc discharge and breakdown of PAO oil film between friction pairs. The Raman spectra showed that the DLC suffered of electrical damage exhibited high graphitization degree, and the extent of graphitization was correlative with the electric currents. Although the graphitization of DLC under electric filed lowered friction in certain conditions, the wear resistance of DLC coating was weakened, so the DLC coating failed in a short time under the combined effects of electrical damage and mechanical wear.