Abstract: In this paper, the diffusion process of Cu3Sn/Cu interface in leadfree solder joints was investigated using molecular dynamics (MD) technique with the modified embedded atomic method (MEAM) potentials. The diffusion behavior of different atoms was analyzed and the diffusion activation energies was obtained. In addition, the thickness of diffusion transition zone was acquired based on the empirical equation of diffusion. The simulation results indicate that the Cu atoms predominantly diffuse into the Cu3Sn side in the process of diffusion. The Cu atoms diffuse slowly but deeply diffuse into the interior of Cu3Sn, whereas the atoms of Cu3Sn diffuse with high rate but hardly diffuse into the interior of Cu. Based on the Arrhenius relation and equation of Einstein, the diffusion activation energies of Cu lattice atoms at interface is 172.76 kJ/mol, and the Cu and Sn atoms in Cu3Sn lattice are 52.48 and 77.86 kJ/mol, respectively.