The effect of lanthanum(La) on nitrogen atom diffusion in ε-Fe3N phase produced during nitriding with and without rare earth addition were studied based on the density function theory of first principles and the quantum mechanics program CASTEP code of Material Studio software.Calculated results show that the presence of La in ε-Fe3N phase can lead to the shrinks of a and b axis and the elongation of c axis of ε-Fe3N crystal cell.The total energy and the stability of the crystal cell with La are lower and higher than that without La,respectively.Diffusion activation energy of nitrogen atom in ε-Fe3N phase with La is 1.01 eV smaller than that in ε-Fe3N phase without La.This is the main reason why rare earth elements diffusing into compound layer produced during nitriding can accelerate the nitriding process or shorten the nitriding duration. The effect of lanthanum (La) on nitrogen atom diffusion in ε-Fe3N phase produced during nitriding with and without rare earth addition were studied based on the density function theory of first principles and the quantum mechanics program CASTEP code of Material Studio software. Calculated results show that the presence of La in ε-Fe3N phase can lead to the shrinks of a and b axis and the elongation of c axis of ε-Fe3N crystal cell. The total energy and the stability of the crystal cell with La are lower and higher than that without La, respectively. Diffus activation energy of nitrogen atom in ε-Fe3N phase with La is 1.01 eV smaller than that in ε-Fe3N phase without La. This is the main reason why rare earth elements diffusing into compound layer produce during nitriding can accelerate the nitriding process or shorten the nitriding duration.