Abstract: The cryogenic tests of rolled AZ61 magnesium alloy were carried out at different time. The effects of cryogenic for different time on the microstructure and mechanical properties of AZ61 magnesium alloy were studied by means of OM,TEM, hardness test, tensile test and fracture morphology observation. The results show that the microstructure of rolled AZ61 magnesium alloy consists of α-Mg and β-Mg₁₇Al₁₂ phases. After cryogenic treatment, the grain size of AZ61 magnesium alloy is obviously refined, the size of β-Mg₁₇Al₁₂ phase decreases, and the number and volume fraction increase. The hardness, tensile strength and yield strength increase slightly, while the elongation increases significantly. The hardness, tensile strength, yield strength and elongation of AZ61 magnesium alloy cryogenic for 24 h are 68.7 HV, 289.1MPa, 192.5 MPa and 22.8% respectively. The elongation is 45.2% higher than that of AZ61 magnesium alloy without cryogenic.