Abstract: In the advanced PWR SGTR accident, the passive residual heat removal system was designed to remove the decay heat in the RCS with a heat exchanger which is immersed in the RWST. The back pressure of the containment used in the analysis will affect the temperature of the RWST water boiling and the temperature difference between the two sides of the heat exchanger, thus affect the heat transfer efficiency. In this paper, the increasing of the containment pressure and temperature caused by the RWST water boiling is analyzed to determine the containment pressure process during the SGTR accident. A comparative research on the accident process under different containment pressure was conducted to determine the effect of the containment pressure on the accident process. The analysis shows that the higher the back pressure of the containment, the smaller the temperature difference between the two sides of the heat exchanger, and the weaker the heat transfer capacity of the passive residual heat removal system. The higher back pressure will prolong the accident process and the end time of the broken flow, increase the amount of coolant released, and decrease the margin of the overflow.