Hierarchical porous carbon has become one of the most competitive electrode materials for supercapacitor. The biomass-derived carbon materials are taken for candidate due to their renewability, sustainability, abundance, and low cost. However, the areal capacitance of carbonized biomass needs to be further improved. Herein, we developed a facile and eco-friendly method for the synthesis of porous carbon from agricultural straw, using carbonizing lignocellulose foams and then KOH activation. The obtained biomass foams were controllably carbonized to form all-carbon material for making the electrode for supercapacitor. The results showed that the as-prepared biomass-derived hierarchical porous carbon (BHPC) materials had a high specific surface area of 772 m(2) g(-1) after KOH activation, and contained the microporous (1.05-1.74 nm) matching with the electrolyte 6 M KOH. The high porosity and the interconnected three-dimensional nanostructure provided efficient migration of the ions in electrolyte, thus the BHPC displayed an outstanding electrochemical performance of supercapacitors. The specific capacitances attained 226.2 F g(-1) (specific surface-area capacitance was 29.3 mu F cm(-2)) at a current density of 0.5 A g(-1) within a potential window of -1.0 to 0 V in a three-electrode system. This work provides a promising approach to realizing the waste straws into a high-valued energy storage material. (C) 2019 Elsevier Ltd. All rights reserved.