In this study, a circulation-type fluidized bed boiler's exergy performance in a power generation plant was investigated. The boiler was examined not as a whole but by dividing it into its sub-systems. In the analysis, the sub-systems' exergy performance was evaluated in terms of criteria such as exergy efficiency, exergy destruction, fuel depletion ratio, relative exergy destruction ratio, exergetic improvement potential, and productivity lack ratio. In addition, the effect of different dead state temperatures on these exergy performance criteria is compared and discussed. As a result of the analysis, the highest exergy efficiency was achieved in the furnace with 80.2% at 6℃, while the highest exergy destruction occurred in the furnace as 18,118.9 kW at 27℃. The highest exergetic improvement potential was realized in Economizer-II with 11,593.82 kW at 6℃, and the lowest in Economizer-I at 27℃ with 631,9 kW. The effect of the increase in the dead state temperature on the exergy performance criteria applied to boiler sub-systems was variable. It showed its effect as an increase in some sub-systems and a decrease in others.