In the present work, carbon composite of two dimensional porous thin carbon nanosheets hybrized with 3D freestanding hierarchical carbon foam (2D-CNs/3D-CF) was successfully fabricated for the first time via a facile impregnation and high temperature annealing strategy. The structure characterizations confirmed that 2D carbon nanosheets with a thickness of ∼8 nm and a plentiful pore channels were successfully assembled on the surface of 3D carbon foam skeleton. With such ultralight, flexible and porous 2D/3D hybrid carbon nanocomposite as active electrode material, a large specific surface area can be available and rapid electron transfer and ionic transport are facilitated. The electrochemical measurements demonstrated that the 2D-CNs/3D-CF-based supercapacitor presents an excellent specific capacitance of 364 F g−1 at 1 A g−1 and even a high specific capacitance of 321.86 F g−1 can be achieved at 10 A g−1 in 6.0 M KOH aqueous solution. Taking a comparison with the previously reported capacitor materials, the as-prepared hybrid carbon exhibited higher capacitance properties. Furthermore, the 2D/3D carbon-based supercapacitor exhibited an energy density of 47.30 Wh kg−1 at a power density of 0.84 kW kg−1 and the energy density can still retain 23.90 Wh kg−1 even when power density runs up to 80.11 kW kg−1 at a relatively high current density of 200 A g−1, demonstrating the superior capacitor performance and extremely high power density and energy density. Such novel carbon nanostructure with 3D freestanding hierarchical carbon foam hybrized with 2D porous carbon nanosheets may have promising application in energy storage devices.