Abstract. The calculated lattice parameters and enthalpies of formation of A1 2 Ca, Al 2 Sr，A1 4 Ca, Al 4 Sr， Mg 2 Ca,and Mg 2 Sr phase in Mg-Al-Ca-Sr alloy system were compared with both calculation results and experimental data published in references available, and the structural stability of these intermetallic compounds phases were estimated from the energetic point of view. The results showed that A1 2 Ca phase had a higher structural stability. After further calculation of lattice parameters and enthalpies of formation of Al 2 (Ca,Sr) phase with Sr and Ca variation respectively, the structural stability of Al 2 (Ca,Sr) phase was predicted from the thermodynamic point of view. The results showed that Al 2 (Ca,Sr) phase had a good alloying ability and the Al 2 (Ca,Sr) with various Ca/Sr atom ratio was either stable, which demonstrated the mutual solubility of Ca and Sr in Al 2 (Ca,Sr) phase. The elastic constants and mechanical parameters for Mg, Al 2 (Ca, Sr) and Al 4 Sr in Mg-5%Al-Ca-Sr alloy were further calculated. Results showed that the obtained elastic constants and mechanical parameters of Mg were accordant with the experimental results and Al 4 Sr is both of the best ductility and plasticity, while Al 2 (Ca, Sr) is both of poorest ductility and plasticity in Mg-Al-Ca-Sr alloy.