The formation enthalpies of the possible precipitates in Mg-Al-RE (Sb) alloy were calculated by thermodynamic Miedema model.The results show that the forming sequence of Al-RE phases is as states next: Al2RE,Al11RE3 and Al4RE in magnesium containing Al when single RE is added.La,Nd,Ce and Y have the same variation tendencies of formation enthalpies for Al-RE phase and the forming orders of Al2Ce,Al2La,Al2Nd and Al2Y are as follows: Al2Y,Al2Ce,Al2Nd and Al2La.In addition,the Mg3Sb2 can take the priority of precipitation in mg-Al-Sb systems,whereas Mg17Al12 is restrained.The RE and Sb microalloyed elements are mainly existed as RESb rather than other phases in Mg-Al-RE-Sb alloy system.The above results were used to analyze the precipitation behavior of the intermetallic compounds in AZ31-RE-Sb alloy.The thermodynamic analysis results agree with the experimental data.