Abstract: This paper is aimed at the upper terminal temperature difference of #7 high pressure heater in a power plant abnormal enlargement phenomenon,combined with the structure of the high-pressure heater and the actual phenomenon in the field,focus on the reason analysis process and methods,The final reason is that there is leakage at the water chamber clapboard of the high pressure heater, forming a "short circuit in the water supply".After treatment, the upper terminal temperature difference of #7 high pressure heater is effectively reduced,at the same time, the economic benefit after the improvement of the upper terminal temperature difference of #7 high pressure heater is roughly estimated.