Abstract: Grid anode cathodic protection system is a new type protection system for the bottom plate of oil tank. Some aspects involved in the design and operation of cathodic protection system applying MMO (Mixed Metal Oxide) grid anode for aboveground storage tank have been discussed. The problems analyzed and discussed include the location of confluence, potential measurement, location of feeding point, calculation of designed current density and selection of reference electrode. Some suggestions on design program and application on this system are given in the paper.