Abstract: Polycrystalline cubic boron nitride (PcBN) was sintered at the high temperature of 1500 ℃ under the pressure of 5.5 GPa, using cubic boron nitride (cBN) powders as the raw materials, Al powders and Si powders as the binders, and nano-diamond as the additive. The effects of nano-diamond mass fraction on the phase composition, microstructure, density, hardness, fracture toughness, and wear ratio of PcBN were investigated. The results show that, the addition of nano-diamond has the great influence on the performance of PcBN. When the diamond mass fraction is 5%, the relative density of PcBN reaches the maximum as 98.5%. Vickers hardness, fracture toughness, and wear ratio of the PcBN samples increase and then drop as the nano-diamond content increases. When the nano-diamond mass fraction is 5%, the hardness, fracture toughness, and wear ratio of PcBN reach the highest values, which are 47 GPa, 4.89 MPa·m^1/2, and 6350, respectively.