This review summarizes the recent advances on the application of 57Fe M?ssbauer spectrometry to study the magnetic and phase characteristics of Nd-Fe-B-based permanent magnets. First of all, the hyperfine structures of the Ce2Fe14B, (Ce, Nd)2Fe14B and MM2Fe14B phases are well-defined by using the model based on the Wigner-Seitz analysis of the crystalstructure. The results show that the isomer shiftδ and the quadrupole splitting?EQ of those 2:14:1 phases show minor changes with the Nd content, while the hyperfine field Bhf increases monotonically with increasing Nd content and its valueis infl uenced by the element segregation and phase separation in the 2:14:1 phase. Then, the hyperfine structures of the lowfraction secondary phases are determined by the 57Fe M?ssbauer spectrometry due to its high sensitivity. On this basis, the content, magnetic behavior, and magnetization of the REFe2 phase, the amorphous grain boundary (GB) phase, and the amorphous worm-like phase, as well as their effects on the magnetic properties, are systematically studied.