Modification of carbon paper by hydrothermal ammoniated treatment for vanadium redox battery was investigated in this paper. The content of nitrogen in the carbon paper improved from 2.957 to 6.432 % due to the introduced of nitrogenous groups. The surface smoothness and morphology of carbon fiber did not change after the hydrothermal ammoniated treatment. In the mean time, the hydrophilicity has been enhanced because of the introduction of nitrogenous groups to the surface of carbon paper. The sample, which was treated at 220 °C for 15 h, shows the best performance in electrochemical activity and charge–discharge among all the samples. At the current density of 20 mA/cm2 after 50th cycles, the coulombic efficiency, voltage efficiency, as well as energy efficiency of the fabricated cell has reached up to 97.2, 85.3, and 82.9 %, respectively. It indicates the hydrothermal ammoniated treatment might be a promising approach to modify carbon paper for vanadium redox battery.