As-cast ingot of Mg-8Li-4Zn-3Y alloy was prepared by fused salt protection in electric-resistance furnace. T4 solid solution and T6 solid solution + aging treatment were carried out on the alloy, and the effects of heat treatment on the microstructure and hardness of Mg-8Li-4Zn-3Y alloy were discussed. The results show that after T4 solid solution, the strengthening phase in the structure decrease, the grain size of alpha-mg phase increase, the morphology become irregular, and the hardness of the alloy decrease. After T5 aging, some reinforced phase particles are precipitated in the structure, and the hardness of the alloy is improved to a certain extent. During the compression process, the Mg-8Li-4Zn-3Y alloy samples all cracked after being drum-shaped and show a shear fracture of 45°.