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The electrochemical properties of Nd2Fe14B single crystal grain,conventional sintered NdFeB and SPS NdFeB in electrolyte were studied. The microstructures and compositions of the magnets were investigated with scanning electron microscope (SEM) and energy dispersive X-ray detector (EDX). Polarization curves in 3.5% NaCl solution show that Nd2Fe14B single crystal grain has displayed most positive corrosion potential and the SPS NdFeB magnet has more noble potentials compared with the conventional sintered one. Compared with conventional sintered NdFeB magnet,SPS processed magnet has original microstructure i.e. the grain size of the Nd2Fe14B main phase is fine and uniform,and the fine Nd-rich phase does not form along the grain boundaries of main phase,but agglomerates into the triple junctions. The pathways for corrosion propagation are restricted and the inter-granular corrosion process though Nd-rich phase in the magnet is suppressed effectively. Therefore,the SPS NdFeB magnet possesses excellent corrosion resistance. Autoclaves test indicates that a strong correlation has been established between an increase in the total rare earth level,which corresponds to the amount of Nd-rich phase,and an increase in the corrosion rate. The results show that chemical character; microstructure and the amount of Nd-rich phase determine the corrosion resistance of magnets and indicate an intergranular corrosion leads to poor corrosion resistance.