The present invention provides a fuel cell power generation system and method, which can realize, at least at one of time periods before start of and after end of power generation, a purging of an atmosphere of a fuel gas flow channel without using nitrogen. Further, it provides a fuel cell power generation system and method, in which a highly dense carbon monoxide can be prevented from flowing into the fuel cell.A fuel cell power generation system is so structured to comprise: a fuel gas generating means for generating a hydrogen-rich fuel gas from a source material having, as a main ingredient, a compound containing carbon and hydrogen; a source material supply source for supplying a source material to the fuel gas generating means; a fuel gas supply means for supplying the fuel gas from the fuel gas generating means to a fuel gas flow channel of a fuel cell at which channel a fuel electrode is placed; and a bypass means for supplying the source material from the source material supply source to the fuel gas flow channel of the fuel cell, bypassing the fuel gas generating means, wherein at least at one of time periods before start of and after end of power generation, the source material, as a displacement gas, is injected into the fuel gas flow channel of the fuel cell via the bypass means.