Abstract: By taking a commercial production semi-continuous casting ZK60 magnesium alloy as the research objection, the effect of deep cryogenic treatment (DCT) at 77 K on the microstructure and mechanical properties was analyzed by means of mechanical property testing equipment, optical microsopy, X-ray diffraction and transmission electron microscopy. The results show that DCT could refine the microstructure, cause some grain orientation and improve the fine second phase precipitates, that resulted in fine grain strengthening and second phase precipitate strengthening. After cryogenic treatment yield strength of the ZK60 magnesium alloy reached from 1505 MPa to 175.8 MPa, the microhardness increased from 65.91 HV to 74.03 HV and the elongation increased from 17.5% to 21.0%.