To investigate the energy characteristics and pressure fluctuations of a twostage double-suction centrifugal pump, the standard k-ε and RNG k-ε turbulent flow models were chosen for the steady and unsteady flow simulations at 0.62, 0.8, 1.0，1.1 and 1.2 designed flow rate conditions. The results showed that the second multiple frequency of the impeller rotation dominated the pressure fluctuations in the suctions. The fluctuation amplitudes for all the monitored points in suctions were very similar and the difference was less than 1%. The second multiple frequency of the impeller rotation also dominated the pressure fluctuations on the impeller blade surfaces where the amplitude became larger than that at suctions. The blade passing frequency dominated the pressure fluctuations in the volute and the largest amplitude was at the point some distance away from the volute tongue. The amplitude of pressure fluctuation increased when the pump operation condition was deviated from the design point. In the volute tongue region, the pressure fluctuation amplitude of blade passing frequency at 1.2 designed flow rate is 1.25 times of the one at designed flow rate, while the ratio at 0.62 designed flow rate is 1.42. 