The internal relationship between the microstructure and service stability of NdFeB magnets was investigated. Results show that the NdFeB magnets after low-pressure sintering have significantly finer grains and more uniform distribution of the Nd-rich phase among the grains, which is beneficial to obtain smaller coercivity temperature coefficients of magnets, thereby improving the temperature stability. Compared with that of the magnets after vacuum sintering, the coercivity temperature coefficient of low-pressure-sintered magnets is reduced from -0.488%/°C to -0.472%/°C. However, the flow of the Nd-rich phase from the triangular grain boundary to the main phase intergranular area promotes the formation of complete network structure, which degrades the corrosion resistance of the magnets. The low-pressure-sintered magnets show more serious corrosion mass loss after immersion in 3.5wt% NaCl solution, presenting a stronger corrosion tendency.