Abstract: A corrosion fatigue test was applied to study the corrosion fatigue crack propagation behavior of LY12CZ aluminum alloy in artificial seawater (3.5wt%NaCl solution). The influences of loading frequency, stress ratio and the pH value of artificial seawater on crack propagation rate were analyzed, and the fracture was observed by SEM to study the mechanism of crack propagation. The test results show that when the loading frequency and pH value decreased, the crack propagation rate increased significantly, and the stress ratio mainly affected the crack propagation behavior in the near-threshold region. Anodic dissolution played an important role in accelerating crack propagation in neutral seawater. However, with the reduction of pH value of artificial seawater the hydrogen replacement reaction at crack tip intensified, and the hydrogen damage of material at crack tip greatly promoted the crack propagation.