Using cBN, TiC and Al as main experimental materials, polycrystalline cubic boron nitride (PCBN) composites were synthesized at high temperature and ultrahigh pressure conditions. The phase composition, microstructure, surface microcracks and various elemental distributions of the composites were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray dispersive spectroscopy (EDS). The microhardness and flexural strength of the material were tested. The research shows that the PCBN sintered body is composed of BN, TiC, AlB2 and AlN at an ultrahigh pressure of 5.5 GPa and a high temperature of 1 450 ℃. The binder is uniformly distributed around the cBN particles, and the cBN particles are firmly bonded together. The hardness of PCBN increases remarkably with the increase of cBN content and the flexural strength increases first and then decreases. The fracture mode of PCBN is the result of the combination of intergranular fracture and transcrystalline fracture.