Abstract: Under the earthquake, there will be fluid-structure interaction effect in the AP1000 passive containment cooling system water storage tank (PCCWST). This will probably threat the integrity of the containment. The PCCWST was simplified into a cylindrical water tank and then designed by Housner’s model. However, the effect of this simplification on impulsive mass remains to be studied. In this study, a fully scaled down PCCWST experiment model and a scale-down PCCWST experiment model with the same volume ratio were designed. Then the shaking table experiments were carried out on these experiment models by measuring the water sloshing frequency, structure’s natural frequency and damping ratio. The impulsive mass and the convective frequency of water in PCCWST were evaluated by the experiment results. Finally, the finite element model of AP1000 concrete containment was built. The water was simulated by solid element by add mass method to simulate the convective effect caused by fluid structure interaction. The modal analysis and transient analysis were conducted for the model. The results were compared with that using other fluid elements (Fluid30 and Fluid80). The study can provide helpful information on design and assessment of PCCWST.