It is important to improve the power generation efficiency of thermal power generation while promoting the location of nuclear power generation to reduce discharge of carbon dioxide from the power generation plants. Software, which effectively examines the performance of the power generation system of various configurations, can contribute to the development of a highly effective, excellent in environmental thermal power generation systems. For this purpose, authors developed a new method to calculate the steady state of power generation systems, such as heat and mass balance, efficiencies, etc. This method is very flexible in calculation condition setting. Then we developed a general-purpose software by which the steady state behavior of the power generation system is analyzed easily.