Abstract: In this paper, the high differential pressure problem on the cooling side of the SEC plate heat exchanger of unit 3 in a nuclear power plant is introduced. By constructing the relationship between the design flow requirements and boundary conditions of the SEC system and the flow resistance coefficient of the heat exchanger, the influence of high differential pressure on the SEC system operation is analyzed. Finally, this problem was successfully solved by increasing the number of plates and adjusting the plate type composition. This method fundamentally eliminated the shortcomings of the plate heat exchanger. It also effectively guaranteed the reliability and safety of the SEC system in long-term operation.Furthermore, relevant experience is valuable for dealing with similar problems of plate heat exchangers in other nuclear power projects.