Three dimensional nitrogen-doped graphene (3DNG) with high nitrogen content and improved electrochemical performance is successfully prepared by a facile, lost-cost hydrothermal method with ammonia as reducing-doping agent. The as-prepared 3DNG exhibits a hierarchical and interconnected porous network, which offers favorable pathways for electrolyte penetration and transportation. Remarkably, as binder-free electrode in aqueous electrolyte, the resultant 3DNG-2 with both high nitrogen content (7.71 at%) and large active material density (1.31gcm−3) exhibits an ultrahigh volumetric capacitance of 437.5Fcm−3 (334.0Fg−1) at current density of 0.5Ag−1 and superior cycling stability (93% capacitance retention after 20 000 cycles at high current density of 10Ag−1). Further analyses indicate that the N-configurations are of great significance to the improvement of electrochemical behavior as well as the N-content. This work provides an effective way to synthesize 3DNG with excellent electrochemical properties for high performance supercapacitor and promotes the in-depth understanding of the enhancement mechanism of N-doping to supercapacitor performance.