With different heat treatment, the microstructure and mechanical properties of ZK60 magnesium alloy were investigated. It can be concluded that heat treatment has great effect on mechanical properties of ZK60. With artificial aging after extruding, the precipitation of the second phase from the supersaturated solid solution significantly improved mechanical properties. It can greatly increase yield strength of ZK60 alloy, while the tensile strength has little change. For the combination of solid solution strengthening and age hardening, two opposite factors must be considered. On one hand, the solid solution strengthening and the later precipitation strengthening is good for alloy’s strength; on the other hand, the properties decrease as the grains grew under high temperature for a long time during solution heating.