Commercial coconut shell-based activated carbon (CSAC) has low specific capacitance and specific capacitance retention owing to its undeveloped pore structure and low proportion of heteroatoms. In this study, dielectric barrier discharge (DBD) plasma was used to enhance the specific capacitance and rate capability of CSAC. H2O was used as excited medium to introduce oxygen functional groups. The physicochemical properties of CSAC and CSAC modified by H2O plasma (HCSAC) were revealed by automated surface area and pore size analysis, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy (Raman). Electrochemical workstation was applied to investigate the electrochemical properties of CSAC and HCSAC. Obtained results showed that plasma modification improved the specific capacitance of CSAC by 64.8% (current density, 1 A g-1; electrolyte, 6 M KOH solution) within 100 seconds. This result is ascribed to the oxygen functional groups introduced to the surface of CSAC. It can also improve hydrophilicity and wettability of the carbon surface leading to an increase from 76.7% to 84.6% in specific capacitance retention. Furthermore, H2O plasma modification can introduce oxygen functional groups without destroying the initial pore structures of CSAC. In summary, we provide a simple, fast, environment-friendly modification method to enhance the electrochemical properties of CSAC.