In the sintered Nd-Fe-B magnets, the forming of various phases, substitution and preference of additive atoms, microstructure and properties, and, most of proce ssing have a close relationship to the thermodynamics. The Al, Cu, Ga, Sn, Zn ha ve positive heat of mixing with the B, the solubility of them in the main phase is small, they react with Nd in the grain boundary and modifying the microstruct ure of the magnets. The Zr, Ti, Nb, W, Mo, V, Cr have large positive heat of mix ing with Nd while have large negative heat of mixing with the B, they can modify the microstructure as well as dilute the magnets. The effects of the common add itional elements on the microstructure, properties and the processes of Nd-Fe-B magnets are discussed in this work by referring the heat of mixing and the binar y diagrams.