With adjustment of energy structure and enhancement of environmental protection standard, gas-steam combined cycle power plants will be erupt gradually, especially with the project of gas being moved from WEST to EAST and liquefied natural gas (LNG)being imported, many more 350MW-class combined cycle power plants will be constructed in China. This paper begins wi discussing on how to choose gas turbine and optimize matching relationship between gas turbine and steam turbine, followed by analyzing application situations and characteristics of heat recovery of steam generators (Hrsg) with supplementary firing equipmen and without, giving several layout programs of steam turbine cycle system, analyzing the chosen method for steam cycle system. analyzing and comparing shafts of combined cycle power plant, analyzing effect on gas turbine performance caused by ambient temperature, providing therefore references to optimize design of large combined cycle power plants.