The invention discloses an organic/inorganic hybrid hardening agent. The hardening agent is characterized by being prepared from the following raw materials by weight: 10 to 50% of a silica sol, 0.1 to 60% of a solvent, 1.5 to 15% of a silane coupling agent containing an unsaturated double bond, 0.1 to 2% of an acidic catalyst and 12 to 70% of an active diluent. The invention further provides a preparation method for the hybrid hardening agent. The preparation method comprises the following steps: after preparation of the raw materials, adding the silica sol and the solvent, then adding the silane coupling agent drop by drop, adjusting a pH value by using the acidic catalyst, carrying out stirring, then adding the active diluent, carrying out rotary evaporation and cooling, continuing evaporation until no fraction is evaporated and then carrying out bottling and aging. The invention also discloses application of the hardening agent in a coating. The hardening agent is used as a film forming substance for a UV-cured nanometer composite coating and for preparation of wear-resistant and scrape-resistant coatings on the surfaces of resin eyeglass and optical discs. According to the invention, the silica sol is modified by using the silane coupling agent containing the unsaturated double bond through a sol-gel process, and a prepared coating has the advantages of environment friendliness, high transparency, high hardness, good wear resistance, etc.