Abstract: A gas turbine intake air cooling system and a method of operating the system are provided. The system can substantially reduce the construction cost for adding the system to a combined plant and improve the reliability of its chiller cooling system by indirectly dispersing exhaust heat from a chiller through an existing plant auxiliary equipment cooling system in the combined plant. The chiller cooling circuit is constructed so that the cooling water to the chiller is extracted through extraction water pipes branched from outlet pipes of heat exchangers composing the plant auxiliary equipment cooling system, and the cooling water heated by the chiller is returned to pipes downstream of the pumps through the returning pipes. In this construction, during operating of the chiller, a back-up division is operated to supply the plant auxiliary equipment cooling water to the chiller. By doing so, the gas turbine intake air system can be operated without affecting the combined plant side.