The present invention provides a method for easily determining the specifications of a fuel cell and a capacitor constituting a fuel cell power generation system according to an operational mode of an electric load connected to the fuel cell power generation system and a fuel cell power generation system having its specification set using the method. The specifications of the fuel cell and the capacitor connected in parallel to the fuel cell are determined by meeting three requirements: the driving performance, the fuel economy, and the durability, in good balance.