The considerable growth of energy demand and limitation of fossil fuels have propelled researchers to try finding a suitable solution to preserve these resources. Some water in the boiler drum is drained to prevent corrosion and erosion of turbine fins, which is called blowdown, causes energy loss in power plant. This research was conducted energy and exergy analysis and exergy destruction of a sample 56 MW steam power plant in response to changes in the mass flow rate of water blowdown from the boiler. The mass flow rates of water blowdown are considered between 1-10% of the mass flow rate which passes from the boiler toward the low pressure heat exchangers called LPH4 and LPH5. The major centers of irreversibility were identified. The results indicated that elevating the turbine input temperature by 100 K resulted in about 11% increase in the turbine exergy efficiency. On the other hand, with the elevation of the condenser pressure by 0.9 MPa, the condenser exergy efficiency diminished by 0.6%. The results also showed that when using a flash tank in the exchangers, the plant had a better status and greater exergy efficiency especially in case of considering water blowdown. The results revealed that in the LPH5, increasing of water blowdown decreases exergy efficiency, while in another exchanger (LPH4) it led to increase exergy efficiency. The maximum exergy efficiency of the cycle was obtained about 32.13% and associated with 10% water blowdown from the boiler toward the LPH4 exchanger.