A novel Nd-Fe-B based permanent magnets named as SPSed NdFeB magnets were prepared by spark plasma sintering (SPS) technique. In order to better comprehend the mechanism of the changes in magnetic properties of the SPSed NdFeB magnets treated in an optimized process, the effects of the heat treatment process on the microstructure of magnets were systematically studied by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDXS)，high-resolution transmission electron microscopy (HRTEM), respectively. The results show that the increase in coercivity of the magnet is related to the obvious decrease in ratio of Fe to RE (Fe/Re) in Re-rich phase，and the RE-rich phase transforms to crystalline state from amorphous state after heat treatment process.