Abstract: Thermal stability and interface diffusion of Si/Ta/NiFe/Cu/NiFe/FeMn/Ta spin-valve have been investigated. The columnar grains are observed by high resolution electron microscopy (HREM). The pinning field increases when annealing temperature is lower than 200℃; when the annealing temperature is higher than 200℃, the pinning field decreases and other properties deteriorates; at 300℃ the pinning field will be zero. From the results of Auger electron spectroscopy(AES), it can conclude that the diffusion among layers is mainly along grain boundary when the annealing temperature is lower than 200℃. The effect of bulk diffusion should be considered at 300℃.