Three-dimensional nitrogen-doped graphene frameworks (3DNGFs) hold great promise in the application of supercapacitors for the advantages of superior conductivity, well-connected porous structure, and additional N-containing active sites for charge storage. Nevertheless, the developed techniques for preparing 3DNGFs always suffer from the drawbacks of high cost or complex processes for large-scale application. Herein, a new and cost-effective method has been developed to massively prepare monolithic 3DNGFs by a simple and scalable electrochemical oxidation process. Benefiting from the enhanced electrical conductivity, the increase in the pore volume for fast diffusion increased the electrode–electrolyte contact area and additional active sites resulting from the incorporation of nitrogen species, the 3DNGFs showed a high specific capacitance of 2250.3 mF/cm2 at 4 mA/cm2, with good rate capability. Furthermore, this 3DNGFs electrode also owns an excellent long-term cycling stability that can retain more than 97.5% of its original capacitance after 10,000 cycles.