Abstract: Cathodic polarization and electrochemical impedance spectroscopy (EIS) were applied to study the changes of protective current density and surface state of high manganese aluminum bronze at different cathodic polarization potentials in seawater.The micro-morphologies and elemental compositions of cathodic polarization products were analyzed by scanning electron microscopy (SEM) and energy spectrum X-ray analysis (EDX).The results show that the surface of high manganese aluminum bronze is covered by the calcareous deposits at polarization potentials of-0.8 V and-0.5 V after 168 hrs of polarizing, and the main component is Ca CO₃.At polarization potential of-0.8 V, iron and manganese oxide is formed on the surface of high manganese aluminum bronze, but the density of the steady protection current is lower, the resistance of the calcareous deposit and the charge transfer resistance are higher, and the structure of the calcareous deposit is more compact.Therefore, the cathodic protection efficiency for high manganese aluminum bronze at the polarization potential of-0.8 V is higher than that at the polarization potential of -0.5 V.