Nanocomposite magnets have become a promising next-generation permanent magnet material due to their potential high magnetic energy product. The implementation of high magnetic performance depends on precise control of the microstructure, including the grain size and distribution of soft and hard magnetic phases, the content of soft magnetic phases, the orientation of hard magnetic phases, the structure and chemical composition, etc. At present, the microstructure of nanocomposite magnets is mainly controlled by adjusting the alloy composition and preparation process. By adding alloying elements, not only can improve the microstructure of nanocomposite permanent magnets, but also can change the intrinsic magnetic parameters of the main phase in the magnet, which is a common method to improve the magnetic performance of the magnet. In this work, the role of alloying elements in microstructure control of RE2Fe14B (RE=Nd, Pr) based nanocomposite permanent magnet materials is summarized and evaluated. The addition of rare earth elements (La, Ce, Pr, Dy, Tb, etc.) to replace Nd atoms alters the intrinsic magnetic parameters of Nd2Fe14B phase. Elements such as Co, Cr, Ni, and Mn can enter the lattice of α-Fe and RE2Fe14B to replace by the point position of Fe, while changing the intrinsic magnetic parameters of the soft and hard magnetic phases, thereby altering the magnetic properties of the magnet. It has been confirmed that elements such as Nb, Ti, and Zr can enter the main phase Nd2Fe14B, but are more enriched at grain boundaries, playing a role in enhancing domain wall pinning and refining grain size. Elements such as Sn and Ga can improve the high-temperature magnetic performance of magnets and enhance their thermal stability. Adjusting the alloy composition through the addition of alloying elements is an effective way to control the microstructure of nanocomposite magnets, but the content of alloying elements should be controlled within a certain range. Excessive addition will deteriorate the magnetic properties of the magnets.