Abstract: The granularity effect for HDDR anisotropy NdFeB powder is studied.The results indicate that the granularity effect for the above powder is low and this powder adapts to preparing for bonded magnet. However, the granularity effect for HDDR anisotropy NdFeB powder is higher than melt-spun NdFeB powder. On the basis of above results, a magnetic powder defect layer model is put forward. The model considers that each magnetic powder consists of surface defect layer, transition layer and main body and that the overall magnetic properties of each magnetic powder result from the magnetic properties of the above each layer of the magnetic powder.