To save freshwater, people want to replace freshwater with seawater for cooling in industry. However, in seawater cooling system, the corrosion of the outlet of heat-exchanger and its following steel components is very serious. Application of Al sacrificial anode is one effective method to prevent steel equipment in seawater from corrosion, but at 50℃, Al anodes in common use are not applicable. So it is important to study the relevant rules governing Al anode performance at high temperature. Since the working potential is an important factor affecting the performance of Al anode, we try to find the rules governing how additional elements affect the working potential at various temperature. Twenty-eight kinds of Al sacrificial anode were made for the experiment by the method of the Chinese National Standard GB4948-85. The interrelation of additional elements in the Al anode and the working potential of anode were studied by the method of grey box analysis. The results showed that the influencing order of elements on the working potential was the same on the whole; and that In, Zn, Mg and Ga were good additional elements for aluminum sacrificial anode in order to get negative working potential.