The coercivity H_c of Nd₂Fe₁₄B magnets and Nd₂Fe₁₄B/(Nd_0.7Dy_0.3)₂Fe₁₄B composite magnets were calculated by computer simulation based on the micromagnetic theory under assumptions that Nd₂Fe₁₄B and (Nd_0.7Dy_0.3)₂Fe₁₄B  grains have magnetically deteriorated layers on their surfaces and diffusion of Dy from (Nd_0.7Dy_0.3)₂Fe₁₄B  grains to Nd₂Fe₁₄B ones through the contacting boundaries recovers the magnetic anisotropy of the deteriorated layers of Nd₂Fe₁₄B grains. H_c of Nd₂Fe₁₄B/(Nd_0.7Dy_0.3)₂Fe₁₄B composite magnets increased by the diffusion of Dy from (Nd_0.7Dy_0.3)₂Fe₁₄B  grains to Nd₂Fe₁₄B ones and the resultant recovery of the anisotropy field of deteriorated layers of Nd2Fe14B grains. The H_c vs fraction of (Nd_0.7Dy_0.3)₂Fe₁₄B  grains curve were convex for the magnets with the degree of alignment between 0.94 and 0.99, which suggests that the above composite magnets have larger H_c values than the alloy-magnets with the same Dy content, and that we can save the consumption of Dy by using these composite magnets.