The invention discloses a preparation method of an ultrathin high strength hydrogel membrane. The preparation method comprises the steps of mixing a hydrophilic monomer, a hydrophobic monomer, an initiator and a solvent A to obtain a mixed liquor, and performing free radical polymerization to obtain a random copolymer solution; and dripping the random copolymer solution into a solvent B, spreading on the surface of the solvent B to form an ultrathin high strength hydrogel membrane, wherein the solvent A is a single solvent or a mixed solvent capable of simultaneously dissolving the hydrophilic monomer, the hydrophobic monomer and the random copolymer, the solvent B is a poor solvent of the random copolymer and is a single solvent or a mixed solvent, and the solvent A and solvent B are much different in surface tension. The hydrogel membrane prepared by the method has the thickness of 10-200mu m, has good mechanical property, can be converted into sol and has repairable function under stimulation of pH, temperature and solvent, and can be used in the fields of medical wound dressing, separating membrane materials, facial mask base materials.