The reasonable regulation of porous structure and crystallinity has been focused on supercapacitor development. Here, hierarchical porous carbons have been prepared by a hybrid of chemical activation and template methods using walnut shells as carbon source, and KMnO4as activator and template agent. The activation mechanism of KMnO4at different activation temperatures has been studied based on the XRD and TG analysis. Due to the synergy of rich oxygen-containing functional groups and hierarchical porous structure, the hierarchical porous carbon materials show a high capacitance of 380 F g−1at 0.5 A g−1, good cycling stability with 93% capacitance retention even after 10000 continuous charge-discharge cycles at 5 A g−1. Additionally, the assembled symmetric supercapacitor has a high energy density of 8.95 Wh kg−1. This study shows that KMnO4activation is a mild and highly efficient way to prepare high performance carbon electrode materials for supercapacitors.Hierarchical porous carbon (HPC) was synthesized using KMnO4as activator and template precursor and walnut shell as carbon precursor by a hybrid of carbonization activation route. Then, the obtained HPCs were optimized to obtain electrode material with the best electrochemical performance, which was applied in the supercapacitor. The activation mechanism of KMnO4was also discussed.