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Here we report an effective and facile method for preparing porous carbons (CSCK-T-x) with highly developed hierarchical porosity for high-performance supercapacitor by one-step KOH activation of coconut shell carbon. The effects of carbonization temperature (T, o C) and KOH/C ratio (x) on the structure and electrochemical properties were studied systematically. The as-prepared CSCK-800-2 displayed two concentrated mesopores at 4 nm and 14 nm. The unique hierarchical structure of CSCK-800-2 enables it to have low ion transport resistance and high ion-accessible surface area, which contributes to outstanding electrochemical performance. Furthermore, it possessed the highest BET speci c surface area of 2143.6 m 2 •g − 1 with a pore volume of 1.34 cm 3 •g − 1 among the CSCK-T-x. In a three-electrode test system, CSCK-800-2 exhibits a high speci c capacitance of 317 F•g − 1 at a current density of 0.5 A•g − 1 and considerable rate retention of 68% at 20 A•g − 1 . The symmetrical supercapacitor that was based on CSCK-800-2 showed a maximum energy density of 13.5 Wh•kg − 1 at 0.5 A•g − 1 in 6M KOH electrolyte. Besides, it also exhibited a superior cycling stability with 99.7% of the capacitance retention after 10000 cycles at 5 A•g − 1 .