Abstract: Using scanning election microscope equipped with X-ray energy dispersion spectrometer and optical microscope the phenomena of diffusion induced grainboundary migration (DIGM) caused by Ag diffusing along the grain boundaries of Cu in Ag(film)/Cu (bulk) diffusion couple annealed at 400℃,480℃ and 580℃ with various times was studied. Based on the characteristics of the migrated boundaries, the diffusion coefficient of Ag in the migrated grain boundary was calculated by an appropriate solution of the diffusion equation for the migrated boundary.