In this work, porous carbon spheres (PCSs) are prepared through hydrothermal treatment of glucose and subsequent chemical activation by KOH. The analysis of pore structure and morphology of the resultant PCSs were characterized by Raman spectra, N-2 sorption technology and electron microscope. The results indicated that the microstructure of activated PCSs can be tuned by varying activation intensity. The PCSs activated at alkali carbon ratio of 4 possess remarkable porosity, extremely large surface area and large pore volume. The well-defined porous structure and high surface area benefited the PCSs to exhibit an excellent charge storage capacity with a specific capacitance of 280 F g(-1) in 6 mol L-1 KOH at a current density of 0.5 A g(-1) and long-term cycling stability over 1000 cycles. The well-developed porous nanostructure together with the excellent electrochemical performances make this study provide new opportunity for hydrothermal carbonization of biomass as electrode materials for energy storage.