To increase the availability of cogeneration, it is desirable to increase the efficiency of power generation from the system, as well as to make the heat-to-power ratio variable corresponding to its demand patterns. A new power recovery system from a gas engine has been invented to attain the purpose. The system utilizes H2O and NH3/H2O mixture. It is a combination of a H2O steam turbine, an NH3/H2O steam turbine, and an NH3/H2O refrigerator. The system can recover power not only from the exhaust gas but also from the jacket water. It can extract power effectively from a high temperature down to a low temperature; 30% or more power can be recovered than when using conventional exhaust gas steam turbine. Moreover, it can change the heat-to-power ratio to conform energy supply to energy demand. This paper describes the concept of the system and the simulation results.