Structural stabilities,thermodynamics stabilities,elastic properties and electronic structures of Mg17Al12,Al2Y and Al4Ba phases were analyzed by first-principles calculations with Castep and Drool3 program based on the density functional theory.The calculated results of heat of formation indicate that Al2Y phase has the strongest alloying ability.The calculated thermodynamic properties show that the thermal stability of these compounds gradually increases in the order of Mg17Al12,Al2Y and Al4Ba phases.Y or Ba addition to the Mg-Al alloys could improve the heat resistance.The calculated bulk modulus B,shear modulus G,elastic modulus E and Poisson ratio v show that the adding Y or Ba to Mg-Al alloys could promote the brittleness and stiffness,and reduce tenacity and plasticity by forming AI4Ba and Al2Y phases.The calculated cohesive energy and density of state (DOS) show that Al2Y has the strongest struetoral stability,then Al4Ba and finally Mg17Al12.The calculated electronic structures show that Al2Y has the strongest structure stability because of the strong ionic bonds and covalent bonds combined action.