The invention discloses a preparation method for high-hardness waterborne polyurethane dispersion. An inorganic nano material and waterborne polyurethane are grafted through an in-situ polymerization method, so that the hybridization reaction of inorganic materials and the organic materials is realized and complementary advantages are realized. The preparation method comprises the following operation steps: adding polyisocyanate, macromolecule polyol, a catalyst, a chain extender and a silane coupling agent according to certain weight ratio in a flask for reacting to obtain a polyurethane prepolymer; after the reaction is ended, sequentially adding a neutralizer, inorganic nano material dispersion liquid and deionized water under the condition of low-temperature and high-speed stirring; finally, heating under the vacuum condition for removing the solvent to obtain the high-hardness waterborne polyurethane dispersion. Compared with the traditional inorganic and organic blending process, the preparation method has the characteristics that products prepared through the preparation method have the advantages of good stability, excellent water resistance, long-time aging resistance, excellent and high adhesion, high drying speed, high hardness, good fullness, higher light transmittance and the like, and are wide in application range.