TiB2-Al2O3 composite was studied by the first principle method. Ti maintains a high positive charge and O increases more charge (absolute value) in the interface, so there is strong ionic interaction among the ions in the interface of TiB2-Al2O3 composite. There is strong covalent interaction among the atoms in the interface of the TiB2-Al2O3. There are some differences of densities of state (DOS) between TiB2- Al2O3 composite and related single phases as the interaction between of TiB2 and Al2O3 phases. The width of DOS of interface Ti 3d is obviously larger than that of inner Ti, and larger than that of TiB2 single phase, which shows that the interaction among atoms in the interface is stronger than that in the center.