The invention provides a rubber reinforcing agent, a preparation method thereof, and a preparation method of butadiene styrene rubber. In the invention, firstly the rubber reinforcing agent having excellent reaction activity with butadiene styrene rubber latex is synthesized in a manner of mixing an aromatic compound containing an alkene unsaturated substituent and an organic siloxane monomer containing an alkene unsaturated substituent, adding an olefin metathesis catalyst and performing a normal-temperature reaction in a methylbenzene solvent with air and water isolated, and removing the methylbenzene solvent through a vacuum desolventizer to prepare the rubber reinforcing agent. The high-strength butadiene styrene rubber is prepared by feeding the rubber reinforcing agent and the butadiene styrene rubber latex into a polymerization kettle according to ratio with addition of an initiator, and performing a reaction for a certain time with reaction temperature controlled, and coagulating, washing and drying the product.