The present invention discloses a method for forming a nano-bubble. The forming method is different from the oil-water emulsion reaction in the prior art. The method comprises: taking an inorganic particle as a nucleus and performing a polymer coating process to coat at least one first polymer on the surface of the nucleus to form an organic/inorganic composite particle; then removing the nucleus of the organic/inorganic composite particle by way of the dissolution of a first solvent to form an impregnated nano-particle; performing a freeze-drying process to remove the first solvent to have the impregnated nano-particle form a hollow nano-particle; and finally dissolving the hollow nano-particle in a second solvent to form the nano-bubble.