The corrosion behavior of auxiliary anode under the combined action of alternating current density and cathodic protection were studied. Firstly, the corrosion rate and corrosion image were analyzed by immersion experiment, and the corrosion process was determined. Secondly, the electrochemical behaviors of the auxiliary anode under different conditions were analyzed by electrochemical test, and the corrosion behaviors of the auxiliary anode under different conditions were characterized according to the change of its corrosion kinetic parameters. The results show that the corrosion product layer formed under lower alternating current density overlays on the surface to slow down the corrosion, while the higher alternating current density can break down the corrosion product layer to activate the corrosion reaction. The cathodic protection current causes the corrosion product layer to be in the constant destruction and the generation process, further promotes the corrosion reaction. The results of immersion experiment are in good agreement with those of electrochemical test.