The effect of eccentricity and whirl frequency ratio on the internal and external characteristics of a centrifugal pump was investigated numerically and experimentally. Under a series of given rotordynamic parameters, the RNG k-ε turbulence model was applied in the simulation of whole flow field including front and back shrouds of pump. The influence of eccentricity on the external characteristics of the centrifugal pump and the impact of whirl frequency ratio on the internal flow field were analyzed. Then the distribution of the fluid-induced forces in the centrifugal pump and the effect of eccentricity and whirl frequency ratio on the fluid-induced forces in the centrifugal pump were investigated. According to the results, it could be drawn that the high efficiency area of centrifugal pump narrows as the eccentricity increases. Normal fluid force component Fn and tangential fluid force component Ft were both approximate into a quadratic function relation against the whirl frequency ratio ω/Ω, influenced by the eccentricity. The fluid-induced forces acting on the impeller were mainly generated by the internal fluid of impeller and uneven circumferential pressure distribution inside. In the centrifugal pump, when ω/Ω>0, vortexes within the impeller were less, hydraulic loss was lower and so restrained the whirling motion; when ω/Ω<0, vortexes within the impeller were more, hydraulic loss was higher and thus promoted the whirling motion.