The invention relates to a preparation method for a nano spherical carbon aerogel, and belongs to the technical field of super capacitors. The preparation method comprises the following steps: mixingan alkaline liquid and alginic acid to form a mixed solution, wherein the alginic acid accounts for 2-10% of the total mass of the mixed solution, adding the mixed solution into acetone or ethanol, performing stirring continuously, performing centrifugation, and performing drying to obtain a nano spherical alginic acid-based carbon aerogel; placing the nano spherical alginic acid-based carbon aerogel into a tube furnace, under the protection of a nitrogen gas, raising the temperature to 500-900 DEG C, performing heat preservation, and performing cooling to room temperature, so as to obtain ancarbonized nano spherical alginic acid-based carbon aerogel; and mixing the carbonized nano spherical alginic acid-based carbon aerogel and KOH, placing the mixed material into a tube furnace, raisingthe temperature to 700-1000 DEG C under the protection of a nitrogen gas, performing heat preservation, and performing cooling to room temperature, so as to obtain the activated nano spherical alginic acid-based carbon aerogel. The activated nano spherical carbon aerogel prepared by the method provided by the invention has a high specific surface area and nano hierarchical structure pores; and the activated nano spherical carbon aerogel is used to prepare a super capacitor, and the prepared super capacitor has characteristics of high specific energy, high power and the like.