An innovative hybrid power generation system involving a structure-solid oxide fuel cell (SOFC) and a proton-exchange membrane fuel cell (PEMFC) is established. A high-temperature SOFC is not only used to produce electricity, but also supplies the reformed gas to a PEMFC to generate extra electricity simultaneously. A steady-state thermodynamic model of the SOFC-PEMFC hybrid system is verified based on the mass and energy balance and the electrochemistry theory. A parametric study is carried out to analyze the effects of various parameters on the performance of the hybrid system. The SOFC operating temperature and the steam-to-carbon ratio have a positive impact on the power output and overall efficiency of the system. The operating pressure benefits the system power output but not the overall efficiency. An optimum SOFC fuel utilization factor exists at the highest value of the power output and overall efficiency of the hybrid system.