The invention provides a binder, a cubic boron nitride polycrystalline sintered body and a preparation method thereof, wherein the binder comprises metal aluminum, silicon dioxide, zirconium carbide,titanium diboride and titanium nitride, the metal aluminum and the silicon dioxide react in the sintering process to form aluminum oxide and elementary silicon, the melting point of the aluminum oxideis far higher than that of the metal aluminum, and the elementary silicon has good thermal conductivity, so that the binding agent can effectively overcome the defects of a metal binding agent and aceramic bonding agent, and the binding agent used for preparing the polycrystalline cubic boron nitride sintered body can effectively improve the hardness, the toughness and the heat conduction performance of a cutter, and has wide adaptability.