Steam-assistant nitrogen (N) and phosphorus (P) co-doping of graphene (s-NPG) architectures are constructed by a facile chemical converted method and thermal activation. Steam-activation treatment can provide abundant porous structure for fast ion diffusion and expose more electrochemical active-sites for surface faradic reaction. The wrinkled surface of S-NPG with a large surface area is probed by microscopic analysis. The spectroscopic analysis confirms the existence of pyridinic- N and C-P-O bonds for s-NPG, which are the dominant electroactive sites for accommodating the protons or charges. Therefore, s-NPG exhibits a high specific capacitance of 317 F g-1 at 1 A g-1 with a good rate capability of 87% and cyclic stability of 97.7% after 20,000 cycles. The excellent pseudocapacitive behavior can be attributed to the synergistic effect of hierarchical structure with and surface modification by N and P dual-doping. The simple steam-assistant treatment can be a potential way to construct the hierarchically structured electrode materials for supercapacitors.