Abstract: A 1 000 MW unit in a newly-built coal-fired power plant adopts a steam-driven feed water pump with a capacity of 100% boiler maximum continuous rating. During commissioning, the shaft seal system of the feed water pump turbine of this unit has the faults of water entrainment of shaft seal steam and abnormal noise of the shaft seal pipe at the side of the feed water pump. Through adjustment and analysis, it is found that the causes of the above-mentioned failures are unreasonable design of shaft seal steam return pipe and imperfect installation of shaft seal steam pipe sleeve in condenser. The fault of shaft seal system of feed water pump turbine has been successfully solved by installing hydrophobic water seal cylinder at the lowest point of shaft seal steam return pipeline and installing heat insulation on shaft seal steam pipeline in condenser.