The biomass-based carbon materials with heteroatomic regulation, hierarchical structure, remarkable porosity, excellent conductivity and good stability are promising energy materials for supercapacitors. Herein, we designed and synthesized the multidimensional morphology controllable carbon materials by activation approach using pervasive watermelon rind as the carbon source. Interestingly, the carbon materials revealed diverse dimensional morphology characterizations for 3D hierarchical honeycomb nanoporous carbon architecture (CNP), 2D carbon nanoflake model (CNF) and 1D needle-shaped carbon nanobars (CNB) with/without different dopants. The CNB energy material indicated a large specific area for 879.18 m2 g−1, and the flexible electrode showed excellent areal capacitance for ∼2245 F cm−2 at 1 mA cm−2. Moreover, the constructed flexible symmetric device shows outstanding cycling stability for 99.5% after 20,000 cycles, superior energy density for 0.12 mWh cm−2 at a power density of 0.52 mW cm−2. This work provides a facile and sustainable approach to synthesize high-performance energy materials for supercapacitor.