The FE analysis to the rotor of a multistage centrifugal pump has been studied based on the software ANSYS. The entity model and FE model of the rotor are built for the static and modal analysis. The model is meshed in two different ways, then the undamped free vibration on rotor is studied including the natural frequencies and mode shapes by comparison. Furthermore, the influence of the fluid-solid coupling action on vibration frequency is discussed. The research in this paper will provide evidence for the structural design and checking of the multistage centrifugal pumps.