The -Fe 3[110] (112) symmetrical tilt grain boundary model is established by the coincidence site lattice theory. First-principles plane wave ultrasoft pseudopotential method based on the density functional theory is used to calculate the La occupying tendency in -Fe. The results show that La elements tend to be located at grain boundary in the -Fe since the impurity formation energy keeps lowest. On this basis, the electronic structure of La doped in -Fe grain boundary is also calculated. The results indicate that the charges in the system are redistributed to provide more electrons for the grain boundary bonding when the La occupies -Fe grain boundary. Meanwhile, Fe atoms obtain more electrons, and the La doped region combination has the ion-tendency toward strengthening the interaction between La atom and Fe atoms in the adjacent boundary region, and the Fe atom bonds in the grain boundaries and on both sides of the grain boundary also strengthen, which is the reason why the mechanical properties change from the energy point of view. Moreover, La addition also makes the atomic density of states on the grain boundary move to the left, reduce the total energy of the system, and make the grain boundary more stable.