Abstract: Compared with traditional large scale pressurized water reactor, the volume of the containment of small pressurized water reactor is small. During a loss of coolant accident (LOCA), the containment pressure of small pressurized water reactor rises rapidly and measures such as pressure suppression pool should be taken to maintain the containment integrity. The pressure suppression pool can be used to quickly relieve the containment pressure, and the containment spray can be used to continuously relieve the containment pressure. However, the existing research on pressure suppression pool is mainly aimed at large scale reactor and mainly focuses on the thermal-hydraulic phenomenon in the containment, and the design scheme of using both containment spray and pressure suppression pool is rarely discussed. In order to investigate the suppressant characteristics of the pressure suppression pool in the suppression containment, the small pressurized water reactor pressure suppression pool and containment spray system simulation facility were modeled, the containment pressure suppression process with the best estimate system computer code RELAP5 was simulated. Condensation and flash evaporation of water could make it difficult to accurately calculate the containment pressure, RELAP5’s capability to simulate pressure changing under different conditions was assessed. The influence of the trend of break discharge on the simulation and design of the pressure suppression pool was analyzed. The suppressant effect of flow area of pressure suppression pipeline and gas-water ratio in pressure suppression pool was compared under different break flow rates and containment spray mass flow rates. The results show that the flow area of pressure suppression pipeline and gas-water ratio in pressure suppression pool have optimal value, and the optimal value of the flow area of pressure suppression pipeline is generally small. The break flow rate is affected by the area of the break. Under the same conditions of total mass and energy release, the faster the break flow rate, the greater the optimal values for the flow area of pressure suppression pipeline and gas-water ratio in pressure suppression pool. The pressure suppression effect will be weakened more obviously if the flow area of pressure suppression pipeline is lower than the optimal value. The continuous pressure suppression ability will be lost if the gas-water ratio is higher than the optimal value. As the containment spray mass flow rate increases, the optimal value for the flow area of pressure suppression pipeline remains unchanged, but the optimal value for the gas-water ratio increases. The research results can provide reference for the design and analysis of the small suppression containment.