The water spraying and cooling device of the exhaust casing is generally used when the exhaust air temperature is 80-120℃ , it can be operated manually too. When the water spraying and cooling device is used, attention should be paid to preventing the temperature of exhaust air room from abruptly decreasing in order to avoid the exhaust casing to shrink too quickly and affect the normal differential expansion of low-pressure casing. Some power plants reflected that the application of water spraying device at low-load operation for long term will bring the spraying water back to the steam side at blade root and will have a certain flushing function on the last stage blade, which shall be noticed.