Based on scattering theory, the resistance of polycrystalline interconnection originates mainly from vacancies and voids scattering at grain boundary. Through using the free volume concept, the scattering process at grain boundary is simulated, and a non-Gaussian model of noise is establised. The model shows the earlier electromigration noise is gaussian, through electromigration process, noise turns non-Gaussian, which reflects the change of dynamic mechanism. Bicoherence coefficient is used to characterize the non-Gaussian noise. Finally, experimental result validates the model.