Effect of solid solution under high pressure on the microstructures and mechanical properties of AM60B alloy has been investigated. The results show that solid solution under high pressure leads to refined crystal grains of α-Mg phase in the alloys after aging treatment. When the solid solution pressure is about 4GPa, the smallest grain size can be obtained, which is only 8.4% of the grain size when the solid solution is carried out under ambient pressure. Moreover, hardness and compressive strength of AM60B after aging treatment both increase remarkably when the solid solution is performed under high pressure. The superior compressive strength and plasticity can be achieved at 5GPa.