This study investigated how the net power generation efficiency varied when its CO2 recovery rate was raised, by taking a combined cycle power generation system as an example. In the system, alkanolamine-based chemical solvent was assumed to be used to remove and recover CO2 from the stack gas, and the extracted steam from the steam turbine at a temperature of 454 K to regenerate CO2-absorbed solvent. The equation to estimate the net power generation efficiency ηN was derived when its CO2 recovery rate R is changed, and a simulation model was developed to estimate various characteristics of the system. It has been estimated that ηN is 50·2% when R is 0%, but the value of ηN degrades sharply according to the rise of the value of R, and ηN decreased to 37·1% when R is raised to 90%; that is, the efficiency of the system becomes lower than 37·7%, that of a CO2-recovering steam turbine generation system using the same chemical CO2 absorption slovent. © 1997 by John Wiley & Sons, Ltd.