In this work, a one-step bimetallic activation method was developed combining the activation performance of metal activators (FeCl3/ZnCl2, FeCl3/MgCl2 and ZnCl2/MgCl2) and etching effect of CO2 to prepare biomass activated carbons from peanut shell for the application in supercapacitors. Results indicate that the loading of ZnCl2 and FeCl3 can produce amount of micropores during biomass pyrolysis, which can provide adsorbing sites for ions. The presence of MgCl2 can promote the formation of mesoporous structure, facilitating the transfer of electrolyte ions. Under suitable conditions, a high specific surface area of 1427.81 m(2)/g was obtained with a large proportion of micropores (73.91%). Graphitic structure was also formed using the bimetallic activation method and partially graphitic porous carbons were obtained, which can simultaneously provide electron pathway and energy storage capabilities. Abundant oxygen-containing functional groups were also obtained on the surface of the carbon samples to further improve their electrochemical performance. All the carbon samples activated at 800 degrees C from bimetallic activation exhibited good electrochemical performance as supercapacitor electrode. The FeCl3/MgCl2 activated sample at 800 degrees C (FE/MG-AC-800) exhibited the maximum discharge specific capacitance of 247.28 F/g at a current density of 1 A/g in the 1 M Na2SO4 electrolyte and good rate capability of 202.34 F/g at 10 A/g. Furthermore, high cyclic stability was also obtained with capacitance retention of 96.31% after 5000 cycles.