Abstract: Abstract: In order to analyze the effect of fluid-structure interaction（FSI）on rotor stress-strain and modal in marine centrifugal pump, a 125clla-13 type marine centrifugal pump was chosen as the research object. The unsteady numerical simulations of uncoupling method and two-way coupling method were used in this paper. Based on the result of simulation, the variation of head in the last rotating cycle was compared between the two simulation methods. The later analysis was focused on the effect of one-way coupling method and two-way coupling method on impeller stress and strain under different transient phases, and further modal multi-phase analysis of rotor was conducted based on FSI. The results show that the predicted value of head with two-way coupling method is bigger than the value with uncoupling method under each transient phase, and there is a local fluctuation of predicted value near the peak of head. The maximum deformation of impeller is located at the back shroud and near the middle area of passage outlet. The maximum equivalent stress is at the border of back shroud and low pressure side of blade outlet, and both the values of impeller maximum deformation and maximum equivalent stress based on two-way coupling method are greater than the values based on one-way coupling method under each transient phase. It means that the styles of fluid-structure interaction have a certain affect on the impeller tress-strain. The position and value of impeller maximum deformation and maximum equivalent stress change with the transient phase. When the middle area of impeller passage sweeps across the tongue, a minimal value of maximum deformation appears, and different FSI methods have different effects on the position of impeller maximum deformation. A maximal value of maximum equivalent stress appears when the blade stays near the area of eighth section of volute, and both the maximal difference values of maximum deformation and maximum equivalent stress between the two methods of FSI appears at 6° phase. The maximal difference value of maximum deformation is 0.17×10-5 m, and the maximal difference value of maximum equivalent stress is 0.296 MPa. The difference of FSI methods has little impact on the rotor modal, but both modal frequency and amplitude of the rotor have a fluctuation in a certain range when transient phase changes, while the maximal fluctuation of frequency is 0.9 Hz, the maximal fluctuation of amplitude is 1.62 mm, and both of them are at the fifth order modal. The research results are useful for the vibration reduction design and structure optimization of the marine centrifugal pump.