Abstract: On the basis of the Navier-Stokes equations and RNG k-ε turbulent model, the numerical simulations of unsteady flow around the tongue region for five flow rates in a centrifugal pump were performed. The pump performances obtained from the unsteady numerical simulations were well coincident with the experiment results. Three monitor points around the tongue region were set to record the time evolution of pressure and velocity variations. The instantaneous vector maps of velocity for three flow rates were captured. The numerical results show that the flow fields are even in the tongue region with small pulsations of pressure and velocity at the design flow rate. The maximum and minimum values of pressure and velocity on monitor points are affected by the well known jet-wake pattern which exists at the impeller exit in the large flow rate. For the small flow rate, there are reverse flows around the tongue tip, back flows from the tongue region to the impeller, and vortexes in the worm section adjacent to the tongue. All these phenomena interacting in the tongue region make the flow complex with considerable fluctuations, where the maximum value of the pressure is 6 times of the minimum value.