A one-step moderate-explosion assisted carbonization strategy is demonstrated for the synthesis of sulfur and nitrogen dual-doped porous carbon nanosheets (CNSs) using the mixture of camellia petals and ammonium persulfate. The ammonium persulfate acts as both explosive and dopant precursor. The prepared porous carbon nanosheets have high BET surface than 1122 m2 g−1 with sulfur and nitrogen contents of 1.34% and 4.89%, respectively, which benefit the improvement of conductivity, wettability and active sites for electrochemical reaction. The electrochemical tests as electrodes materials for supercapacitor, lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs) indicate that the prepared sulfur and nitrogen dual-doped porous carbon nanosheets possess superior energy-storage performance. The specific capacitances of the CNS–800 symmetric two-electrode supercapacitors using 6 M KOH liquid and KOH/PVA solid-state electrolytes for high current density of 20 A g−1 are up to 176.2 F g−1 and 136.0 F g−1, respectively. The CNS–800 anodes exhibit high capacities as well as good cycle performance with capacitance of 310 mA h g−1 and 129 mA h g−1 after 1000 cycles at 0.2 A g−1 for LIBs and SIBs, respectively. The results provide a novel route for low-cost and large-scale production of CNSs electrode materials for high-performance electrochemical energy storage devices.