This paper studies the doping of Mg2Si by alloying elements Bi from the kinetic point of view. the occupancy. The occupancy, structural stability, elastic properties and electronic structure of alloying element Bi-doped Mg2Si phase were discussed by the first principle calculations, which based on density functional theory in CASTEP program.The calculated results show that Mg2Si,Mg7Si4Bi and Mg8Si3Bi can be stable and the interstitial solid solution Mg8Si4Bi is unstable in the system, the Bi atoms preferentially occupy the Si atoms in the Mg2Si crystal; Mg2Si, Mg7Si4Bi, Mg8Si3Bi are all brittle phase. The ductility, alloying ability and electrical conductivity of Mg2Si can be improved by doping alloying elemen; The essence to the bonding of Mg2Si is a combination of metal bonds, covalent bonds and ionic bonds, Bi-Si and Bi-Mg bonds are formed in Mg2Si phase by doping Bi atoms, which are beneficial to improve the stability of the system.