The dynamic stress analysis for a large double-suction centrifugal pump impeller was presented by using the finite element method. This analysis was based on the sequential fluid-structure interaction theory. The pressure pulsation obtained from flow simulation by using CFD code was set as the force boundary condition. The dynamic stress characteristics of the impeller under five flow conditions (0.6Qd, 0.8Qd, Qd, 1.1Qd, 1.2Qd) were given. The results showed that the maximum stress of the impeller appeared at trailing edge or leading edge region of the blade near shroud. The stress distributions on impeller blade surfaces under different flow rate conditions are similar to each other. The level of dynamic stress under 0.6Qd is the highest. The dynamic stress varies periodically with the impeller rotating. It is also found that the fundamental frequencies of the dynamic stress are the rotating frequency and its harmonic frequency.