In this paper, Magnetic high frequency induction heating method is used to prepare the high quality magnesium-lithium alloys. The effects of Si-Nd co-addition on microstructures and mechanical properties of Mg-11Li-3Al alloy were studied. The results indicate that two main second phase Mg2Si and Al11Nd3 were formed in the alloys adding Si and Nd elements. The added Si element can promote the formation of a black precipitate morphology Chinese characters gathering area, and Nd can refine the rod-like black precipitates and reduce the grain size, clean tissue. When the addition amount of Nd was 1 wt%, the best refinement was obtained. The XRD and EDS analysis found that the rod-like black precipitates were combined phases of Mg2Si and Al11Nd3. The tensile strength of the as-cast alloys increase with the Si content and finally level off. The plasticity will not change monotonously with a certain or compound element. The Mg-11Li-3Al-1Si-1Nd alloy acquires the best comprehensive mechanical properties, its tensile strength and elongation reach 212.3 MPa and 46.2 %, respectively.