For the potential new permanent magnet materials, SmFe12-based compounds, Ti plays an important role in stabilizing the SmFe12-based structures. Thermodynamic properties of the systems relating to Sm–Fe–Ti ternary system become indispensable for the future development of the SmFe12-based magnets. In order to construct the multi-component thermodynamic database for SmFe12-based compounds, the thermodynamic properties and phase diagram of Sm–Ti binary system is necessary. In this work, we attempted to construct the Sm–Ti binary thermodynamic database using data obtained mainly from first-principles. First-principles calculations are performed to obtain the Gibbs energy of ordered and disordered structures within the binary system and used for parameterized the Gibbs energy descriptions of various phases in the Sm–Ti binary system through the CALPHAD methodology, the first Sm–Ti phase diagram has been calculated accordingly.