In order to research the influence of doping lanthanon on Ti-Al series ductility in room temperature, based on first-principles full potential linearized augmented plan wave method, we use generalized gradient approximation (GGA) and local density approximation (LDA) to build a unit cell model, and use Castep to calculate and analyze TiAl structure doped with Sm, La, structure and mechanical property of intrinsic TiAl and doped TiAl. The data show that as TiAl has been doped with Sm, covalency of TiAl is enhanced, bonding directivity and hardness are improved; ionicity is declined and ductility is reduced. As TiAl has been doped with La, covalency of TiAl is declined, bonding directivity and hardness are reduced; ionicity is enhanced and ductility is improved. Therefore, doping intermetallic compounds with lanthanon may improve mechanical property, it is a promising research direction.