Abstract: It is normal that the outside of metal tank bottom plate is seriously corroded and that the insulated flanges must be installed by the traditional method of cathodic protection. However, recent study shows that the solid electrolyte with impressed current is available for use in the principle of cathodic protection, and that the tank bottom plate is being cathodically polarized. By this way, the purpose of retarding or controlling corrosion could be achieved with polarized potential controlled at a setting value and the installation of insulated flange could be eliminated.