Abstract: In the hot commissioning of Fangjiashan nuclear power project, a relatively large temperature difference was found between the two ends of the deaerator in the feedwater deaerator system（ADG）. Displays in the main control room show that the temperature difference was nearly 40 degrees. After a detailed analysis, this paper found the cause for the temperature difference and put forward a variety of solutions. Through argumentation comparison, a deaerator recirculation pump was added, which successfully solved the problem in the start-up phase.