The invention relates to a preparation method of nano-composite hydrogel, belonging to the technical field of hydrogel preparation. The preparation method of the nano-composite hydrogel comprises the following steps: (1) carrying out acidolysis on chitin with acetylation degree of 0.94 to obtain chitin nano-whisker reinforcing agent dispersion; (2) mixing the chitin nano-whisker reinforcing agent dispersion with a gelatin solution, and cooling to obtain the nano-composite hydrogel. The nano-composite hydrogel prepared by the method is good in mechanical properties and high in gelatinization temperature, and has very good stability in the environment with strong acidity and high salt ion concentration, thus being wide applied to the fields of food, cosmetics and medicines.