In this paper, a single solid oxide fuel cell with internal reforming and parallel flow is modeled and optimized. The single fuel cell is a part of a stack of fuel cell system used for cogeneration of heat and work. The governing equations including the conservation equations of mass, momentum, energy and electrochemistry relations are solved by gPROMS software and validated using the data available in literatures. The effect of quantities such as the rate of fuel consumption, the amount of excess air and the percentage of pre reforming of fuel on the power and the efficiency of the fuel cell were evaluated. The results show that the percentage of the fuel pre reforming on the performance of fuel cell is more effective than other parameters and the power output and energy efficiency increase with increase of it. Optimal working point of fuel cell with three objective functions (output power, the product of output voltage in voltage efficiency and output power in energy efficiency) has been obtained. The optimal current density is less than the current density of maximum power output. the optimal power output and energy efficiency with considering minimum energy dissipation are 1.11W/cm2 and 42% respectively and with considering minimum exergy are 1.46 W/cm2 and 24%, respectively.