This paper aims to analyze the behavior of the isolated containment vessel for the nuclear power plant under earthquake considering soil-structure interaction (SSI) and to optimize the number of isolation bearings. Therefore, a three-dimensional finite element model is established for CPR1000, and ABAQUS is used to simulate the seismic acceleration and displacement response under the LBNS seismic wave. The simulation conditions are: analysis with and without SSI, isolated and non-isolated structure, and different number of lead rubber bearings. For non-isolated containment, after considering the SSI effect, the maximum acceleration response decreases by 44.39%, and the maximum displacement response increases by 27.03%. For the isolated structure, the influence of SSI effect is relatively small, and the changes in maximum acceleration and displacement response are 3.17% and 10.73%, respectively. However, the SSI effect cannot be ignored when considering the displacement response. With the increase in the number of isolation bearings, the stiffness and damping of the isolation layer increases. As a result, the maximum acceleration response of the containment increases linearly. The maximum displacement response declines rapidly when the number of bearings decreases from 100 to 300. Then it slows down when the number rises above 300. That means the decrease of displacement response is not obvious at this stage, while the acceleration response will increase. Therefore, 300 is relatively the optimal number for isolation bearings.