The microstructure and phase composition of Mg-9.5Li-2.56Al-2.58Zn alloy were studied. At the same time, the UTM5305 electronic universal testing machine was used to carry out the compression experiments with different strain rate and different deformation amount, to obtain the true stress-strain curve, and to construct the room temperature deformation constitutive equation of the alloy. The microstructure and mechanical properties of the alloy before and after compression were studied.The results show that Mg-9.5Li-2.56Al-2.58Zn alloy consists of five phases: α-Mg, β-Li, Al12Mg17, AlLi and MgLiAl2. β-Li is the matrix phase, α-Mg phase is strip or block, fibrous Al12Mg17 phase is in the interior of α-Mg phase, granular MgLiAl2 phase is distributed on the grain boundary, and intragranular AlLi phase is granular. After solution treatment, the number of precipitates in the alloy structure decreased obviously, and the strength of the alloy increased. According to the real stress-strain curve of Mg-9.5Li-2.56Al-2.58Zn alloy, the effect of strain rate on the flow stress is analyzed. There are peak stress and softening phenomenon after peak value in the compression of extruded and solid solution alloy at room temperature, which is conducive to room temperature forming. The constitutive equation constants n and LnA-(Q/RT) in different states are obtained by linear regression, and the constitutive equation based on Arrhenius model is constructed. With the increase of deformation, the microstructure of the alloy is gradually flattened and elongated, and the AlLi phase is increased.