Abstract: Strengthening the surface of a piston ring can reduce friction and wear of the piston ring cylinder liner and improve engine efficiency, which is an important way and guarantee for the realization of the low-carbon strategy of commercial vehicles. In order to improve the performance of the piston ring, this paper carries out a research on the surface modification of the piston ring by means of liquid-phase Plasma Electrolytic Carburizing and Boronizing (PEC/B) technology. Then, the effects of the operating parameters on the surface morphology, hardness, phase composition, cross-sectional morphology, element distribution and tribological properties of the workpieces are systematically explored. The research results show that the modified PEC/B layer is mainly composed of a boronized layer and a carburized transition layer. The main composition phase of the boronized layer is Fe2B, and that of the carburized transition layer is Fe3C. Boronizing efficiency can be effectively improved by carburizing treatment. The maximum thickness of the modified layer can reach more than 15 μm, and the maximum hardness of the boronized layer can reach 1 460HV. After PEC/B modification treatment, the friction factor and weight loss rate of the workpieces are about 11% and 7% of those of the untreated ones, and the tribological performance significantly improves. It shows that liquid-phase PEC/B can provide a feasible technical way to improve the performance of piston rings.