Abstract: The features of largescale gassteam combined cycle generator unit were introduced. Combining with practical example, the type selecting process of the combined cycle generator unit was analyzed. The influences of the unit capacity, the energy price and annual run hours of the unit on the investment payoff period were analyzed, which can be used as reference for unit type selection.

Key words: nature gas, gas-steam combined cycle, generator unit,  cogeneration, analysis on type selection