The changes in exhaust pressure is greatly effect the economy, safety on turbine performance, the improvement of vacuum, can reduce the consumption of steam turbine and get more of the economy, the higher the condenser vacuum, the lower exhaust steam pressure, the more the steam heat energy into mechanical energy, the less heat is taken away by the circulating water, condenser pressure each reduce 1Kpa, turbine load will increase about 2% of rated load. Vacuum is not the higher the better, the higher the vacuum, the more energy consumption circulating pump. The higher the vacuum, the higher the last stage humidity, the axial thrust increases. If condenser vacuum deterioration, exhaust pressure increases, the more heat of the steam in the heat is taken away by the circulating water, the more heat loss, the same steam flow, the same initial parameters, it can not be brought to the rated load value. Such as maintaining the rated load steam flow rate increases, the blade will be overloaded, the axial thrust increases, so the unit should be maintain economic vacuum in order to obtain a better economy in operation.