Abstract: The sintering mechanism was investigated for (SiC, TiB₂)/B₄C matrix composites fabricated under hot pressing conditions. It is believed that the sintering mechanism is liquid phase sintering caused by the addition of the sintering additive in this research system. The micro particles in the powders in the system worked out a significant contribution to the sintering compaction of the composites. And the phase composition, microstructure, and mechanical properties of the composites were measured and analyzed. The results show that SiC, TiB₂ and a bit of BN are produced by sintering reaction at sintering temperature 1800~1880℃, pressure 30 MPa with original powders B₄C, Si₃N₄, a little of SiC and TiC and the sintering additive of (Al₂O₃ +Y₂O₃). The microstructure of the crystal formed in the system is sandwich. The hardness, bending strength and fracture toughness of the fabricated samples are HRA88.6, 540 MPa and 5.6 MPa·m^1/2, respectively.