3D nitrogen-doped graphene (NRG) was prepared in the hydrothermal method with graphene oxide (GO) as the raw material and melamine as the nitrogenous source and reducing agent. Scanning electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, nitrogen adsorption-desorption analysis and electrochemical measurements were used to characterize the morphology, structure, components and supercapacitor performance of as-prepared electrode materials. The results showed that GO could be reduced efficiently by melamine and realized N-doping at the same time. The 3D structure was built due to the strong interaction between graphene sheets. Its content of nitrogen atoms was 4.37%. The electrochemical performance was measured through electrochemical tests. When the mass ratio of GO and melamine was 1∶2 (NRG-2), the highest specific capacitance of 296 F/g can be achieved at the current density of 1 A/g, which was higher than the capacitance of other mass ratios of GO and melamine. 88.5% of the capacitance of NRG-2 remained after 1000 cycles, which meant that NRG-2 had a long life cycle.