Abstract: Abstract: In recent years, nuclear power has drawn increased attention because of its high efficiency and low pollution. Thus, a rising number of nuclear power stations are being constructed. The safety of nuclear station operations is mainly guaranteed by the residual heat removal system. Residual heat removal pumps (RHRP) are operated when the nuclear main pump stops working and the nuclear station needs to be maintained. The RHRP works in a complex environment, and its work status directly affects the performance of the entire plant. To ensure the reliability of the RHRP, the vibration characteristics of the rotor were analyzed using fluid-structure interaction theory. Stress and deformation analysis by partitioned solution for an impeller in a moving fluid was performed, and modal analysis of the impeller by monolithic solution was conducted in still fluid. For the partitioned method, there are two strategies for coupled solutions of dynamic fluid and structure interaction, one-way coupling and two-way coupling. Two-way coupling is typically used for large structural deformations. One-way coupling is suitable for the small structural deformation cases. In pump machinery, the impeller vibration caused by unsteady flow results in small deformations. Additionally, the feedback of the impeller motion onto the flow is small and therefore, can be neglected for most cases. Consequently, one-way coupling has been chosen, in which dynamic forces are transferred to the structure through the interface in a single direction at every time step. To understand the influence of the impeller shroud thickness on the resulting vibration characteristics, three impeller modifications were investigated and compared to the initial geometry under different flow rates. Moreover, five commonly used materials for an impeller were also evaluated. The three-dimensional turbulent flow was modeled utilizing a SST k-ω turbulence model, and the numerical results were verified by the experimental data. The results showed that due to local structural differences between the pumps used in the numerical calculation model and the test measurement, as well as other effects, such as mesh quality, it was inevitable that there would be differences between the numerical calculation and the test measurements. However, the overall external characteristics of the numerical simulation were generally consistent with the performance of the test measurements, indicating that the flow-field calculation model can accurately predict its performance. By comparing with impellers adapted from four other materials and different shroud thicknesses, the vibration modes of the impellers were basically same for each order; however, the natural frequencies differed to some extent. The first order frequency of original impeller rotor was 394.17 Hz at hot condition and increased by 2.28% compared with cold condition, which was higher than blade passing frequency. Natural frequency of 1Cr13MoS was the highest among employed materials for each order mode, while ZG225-450 was the lowest. At design and off-design flow rates, the stress and displacement fields were similar. The displacement grew from the hub to the outer diameter, and each blade passage had a local maximum on the rear shroud. Moreover, the higher equivalent stress values can be observed in the junction between blade and shroud. Under three operating points, the peak values of stresses occurred in the middle of the junction between shroud and blade pressure side. Decreasing the head caused a significant reduction at the beginning of the blade passage. The stresses along defined paths were almost independent of the front shroud thickness, but peak values could be significantly reduced with a thicker rear shroud. The trendy of stress distribution between hot and cold condition was basically same. However, stress of hot condition was higher than cold one. Especially nearby the leading edge of the impeller, stress of hot condition increased more than 300%, compared to cold one. The results provide a theoretical basis for improving system performance and further study for more complicated dynamic analysis and fatigue analysis.