Abstract: The solid solution model of Mg₁₅X （X=Mg,Al,Zn,Ca,Nd,Er） was constructed by Castep software based on density functional theory,and the lattice constant,structural stability and electronic characteristics of the soulid solution were calculated by first principles.The results show that in contrast to the Mg₁₆structure,the c/a values of Mg₁₅X（X=Al,Zn,Ca,Nd,Er） solid solution structures decrease,and the reducing amplitude of c/a for Mg₁₅Nd and Mg₁₅Er is more than other solid solution structures.So,it can be predicted that the ductility of magnesium alloy improves by adding appropriate amount of rare earth element,Nd or Er.The calculated values of forming heat and cohesive energy of Mg₁₅X（X=Mg,Al,Zn,Ca,Nd,Er）solid solution structures are negative,indicating that the solid solution structures can exist stably.Furthermore,the solid solution strengthening of Al,Nd and Er in magnesium alloy is stronger than that of Ca and Zn.In addition,the electron mechanism of Mg₁₅Er and Mg₁₅Nd structures with excellent stability is that Mg（s） and （p） are strongly hybridized with valence electrons in Er（d）,（f）,Nd （d） and （f） orbitals respectively,showing strong covalent bond.