Power demand patterns, such as for houses, fluctuate sharply. Therefore, if fuel cell cogeneration is installed in a house, partial-load operations with low efficiency frequently occur. On the other hand, if the hydrogen rate of hydrogenation gas-engine generation is increased at the time of low load, emission cleanup and brake thermal efficiency improve. So, in this paper, a hybrid cogeneration system that combines a hydrogenation gas engine and a solid polymer membrane-type fuel cell is proposed. So, operation of a fuel cell or a gas engine with the threshold value of load is investigated. In this paper, four systems were investigated by numerical analysis: independent hydrogenation gas-engine operation, solid polymer membrane-type fuel cell independent operation, that operates a fuel cell or a gas engine with the threshold value of load, and operation using a fuel cell to a base load. As a result, the operating method corresponding to a base load in polymer membrane-type fuel cell had the highest total efficiency. In this case, gas-engine generator (NEG) is operated corresponding to load fluctuation. Moreover, in the comparison results of carbon dioxide emissions, the hydrogenation operation of NEG achieved the best result.