The electronic parameters，such as the structural energy and atom binding energy of both α-Mg and α-Zr，the Mg/Zr interface energy and surface energy of Mg，as well as the interaction energies between Zr atoms and between Zr and impurity atoms，were calculated by means of recursion method. The calculated results showed that the structural energy and atom binding energy of α-Zr are lower than those of α-Mg，and the Mg/Zr interface energy is lower than the surface energy of Mg，which，in an energetical point，explains the experimental phenomenon. Specifically，Zr particles first crystallize out of the Mg liquid and then act as heterogeneous nucleation sites to refine the Mg grains. The atom interaction energies indicate that the Zr atoms can attract each other to form Zr atom clusters in Mg，and combine with impurity atoms to form compounds，thus weakening the Mg grain refining effect.