Mg-Li alloys are the lightest metallic engineering structural materials at present, and have great application potential in 3C and autonomous smart wearable, etc. However, the engineering application of ultralight Mg-Li alloys is seriously restricted because of their low strength, poor stability and high temperature performance. It is difficult to coordinate their strength, plasticity and high temperature performance. Ultralight Mg-Li-Al-Sn, Mg-Li-Al-Mn and Mg-Li-Al-Ca alloys with high strength and good ductility have been developed in our research group. The microstructure, mechanical properties of Mg-Li-Al-X alloys were investigated systematically combing the usage of many advanced microstructure characterization methods and normal tensile tests, etc. Element segregation and strain induced precipitation reaction phenomenon was found, which is beneficial to the improvement of strength and ductility, which is beneficial to obtain high strength and good plasticity simultaneously. The results from this research provide important technological support for the controlling of microstructure and mechanical properties of Mg-Li alloys.