The present invention relates to a method for synthesizing superparamagnetic ferroferric oxide nano-sheets. The method comprises: adding a trivalent soluble iron salt and a divalent soluble iron salt to hydrochloric acid to form a uniform mixed solution, adding the mixed solution to a NaOH solution in a dropwise manner under vigorous stirring, carrying out magnetic attraction on the precipitate after completely reacting, washing a plurality of times with deionized water and ethanol, and carrying out vacuum drying at a temperature of 50-90 DEG C to obtain the superparamagnetic ferroferric oxide nano-sheets. Compared with the method in the prior art, the method of the present invention has characteristics of simple operation, no requirement of inert gas protection, performing at the room temperature, simple reaction conditions and easy operation. The superparamagnetic ferroferric oxide nano-sheets prepared by adopting the reversed-phase co-precipitation method have the small particle, the diameter of 10-30 nm, the saturation magnetization of 77.8 emu/g, and the residual magnetism of 0, and have the superparamagnetism so as to be easily used in the field of biomedicine and bioengineering.