The invention relates to a method for preparing an electrode material of a supercapacitor from mimosa pudica. The method mainly includes the steps that mimosa pudica is freeze-dried in vacuum, carbonized at the low temperature of 200 DEG C-400 DEG C and then carbonized at the low temperature of 600 DEG C-800 DEG C in a tube type resistance furnace, biochar and analytically pure potassium hydroxide are mixed uniformly by the mass ratio of 1:0.5-4 and carbonized for 0.5-3 h at the constant temperature ranging from 600 DEG C to 900 DEG C in a box-type atmosphere furnace, and an activated product is subjected to acid treatment, centrifugally washed to be neutral and dried to obtain the electrode material of the supercapacitor. The method is simple in synthesis step, relative moderate in reaction condition, high in repeatability, high in yield and easy to industrialize on a large scale; the specific surface area of the prepared electrode material of the supercapacitor reaches up to 1307 m<2>/g, the measured capacitance reaches up to 250 F/g under the current density of 1A/g in a 6M KOH solution, cycling stability is good, and the electrode material of the supercapacitor is relatively ideal.