The invention provides a rubber reinforcing agent and a preparation method thereof and provides a preparation method for high-strength nitrile butadiene rubber through ternary polymerization of acrylonitrile, butadiene and the rubber reinforcing agent. In the invention, firstly a nitrile butadiene rubber reinforcing agent having excellent reaction activity with both the acrylonitrile and butadiene is synthesized through the steps of: mixing a nitrile compound containing an alkene unsaturated substituent group and an organic silioxane monomer containing an alkene unsaturated substituent group; with a methylbenzene solvent, adding an olefin metathesis catalyst, insulating air and water, and performing a reaction at normal temperature; and removing the solvent through a vacuum solvent removal device to prepare the nitrile butadiene rubber reinforcing agent. The reinforced nitrile butadiene rubber is prepared by adding the acrylonitrile, the butadiene and the nitrile butadiene rubber reinforcing agent into a polymerization kettle according to ratio, adding an emulsifier, soft water and an initiator, controlling reaction temperature and pressure, and performing a reaction for a certain time, performing condensation, and washing and drying a product to prepare the high-strength nitrile butadiene rubber.