Abstract: Based on the observations of TEM, a microstructural model of Sintered NdFeB magnets has been found. The coercivity of the model was calcu-latedbased on micromagnetic theory and the coercivity of both Nd₂Fe₁₄B grains and sintered NdFeB magnets were analysed and discussed. A magnetic hardering theory of epitaxial layer of Nd₂Fe₁₄B grain and the way of increasing coercivity of sintered NdFeB magnets were put forward.