Oxygen functional groups are one of the most important subjects in the study of electrochemical properties of carbon materials which not only can change the wettability, conductivity and pore size distributions of carbon materials, but also can occur redox reactions. In the electrode materials of carbon-based supercapacitors, the oxygen functional groups have been widely used to improve the capacitive performance. In this paper, we systematically analyzed the reasons for the increase of the capacity that promoted by oxygen functional groups in the charge∕discharge cycling tests and the mechanism how the pseudocapacitance is provided by the oxygen functional groups in the acid/alkaline aqueous electrolyte. In addition, we in more depth discussed the effect of the oxygen functional groups in electrochemical impedance spectroscopy.