Site substations of Y and the super-cell systems of γ-TiAl doped with Y were investigated by the means of the first-principle plane-wace pseudopotential method based on density functual theory. The geometric and electronic structures, the formation energy, Mulliken and bond population of Ti2Al2, TiAl2Y, Ti3Al4Y, Ti7Al8Y as well as Ti15Al16Y were obtained. The results show that Y prefers to be a substitute for Ti in γ-TiAl alloy. The addition of Y increases both lattice distortion of γ-TiAl and forming ability of the doped lattice. Moreover, the proportion of covalent properties increases first and then desends with increasing Y doping concentration. Ti15Al16Y possesses the lowest proportion of covelent properties, improving the brittleness of γ-TiAl.