This paper studies the electric potential of Solid Oxide Fuel Cell(SOFC).The activation over-potential,ohmic over-potential and concentration over-potential are solved by recently published equations.This paper also discusses the influence of operating temperature and steam to the SOFC's operating cell potential.Through the research,it is found that the temperature have great influence on SOFC's cell voltage.When the current density is high,the SOFC's cell voltage is higher with higher operating temperature.The steam ratio of the fuel have effects on SOFC's ideal electric potential and over-potentials.In summary,the less the steam ratio is,the greater the cell voltage we can achieve.