The static and dynamic mechanical responses of Mg-Li alloy prepared by vacuum induction melting were investigated by split Hopkinson pressure bar (SHPB) under the strain rates of 1.7×10-3-1026 s-1, and the stress-strain curves under different strain rates were obtained. Based on the SHPB experimental results, the constitutive relation of this alloy under one-dimensional stress high strain rates impact was fitted. Besides, the metallurgical structure of the Mg-Li alloy after impact under different strain rates was also analyzed. Results show that the dynamic impact properties of the Mg-Li alloy are not sensitive to the strain rate. The constitutive relation of the Mg-Li alloy under one-dimensional stress high strain rates impact is σ=1.5ε (σ<0.12 GPa), and σ=0.12+2.7ε1.2 (σ≥0.12 GPa). With increase of the strain rate, the grains become smaller at first and then tend to be irregular shapes. The short-strip compounds are concentrated distributing in the boundaries.