Combined cycle plants which feature distinct advantages for power generation such as fast response, high efficiency, environmental friendliness, fuel flexiblity represent the majority of new generating plant installations across the globe. Combined cycle plants have different operating modes where the operating parameters can differ greatly depending which mode is operating at the time. This paper addresses the bidding strategy model of combined cycle plants in a competitive electricity market by using a characteristic of multiple operating modes of combined cycle plants. Simulation results of case studies show that an operating mode among multiple ones is selected strategically in generation bidding for more profit of generation company.