Ti is an important active element in Ag-based and Sn-based filler metals to join α-Al2O3. Therefore, the bonding mechanism of Ti and Al2O3 was studied by using first principle calculation. Three kinds of interfaces with different termination and stoichiometric ratio were studied by using the results of work of separation (Wsep), electronic structure and interface energy. It is found that in the O-terminated interface, Ti and O atoms form strong ionic-covalent bonding, resulting in largest Wsep of 12.26 J/m2. In the Al2-terminated interface, Ti and Al atoms form metallic bonding, with small degree of ionic and covalent, and the Wsep is 3.18 J/m2. In the Al1-T interface, both Ti–O and Ti–Al bonds form at the interface, and the Wsep is 4.06 J/m2. The interface energy was calculated as a function of activity of Al and oxygen partial pressure at the temperature of 573K and 1173K. At the temperature of 573K, the stoichiometric interface has lowest interface energy within the PO2 range of e−10∼e+33 Pa. Under the experimental condition, the stoichiometric interface is more stable. While, at a higher temperature of 1173K, when the PO2>∼e−11.8 Pa, the O-rich interface has lower interface energy. The Ti–O compounds are more favored at the interface under the experimental condition.