To investigate the hydraulic characteristics of a shaft tubular pump, the flow field and the pressure fluctuations at the impeller inlet, numerical simulation based on URANS method and a curvature corrected SST k-ω turbulence model was used to simulate the unsteady internal flow field in a shaft tubular pump with and without the groove control technique. The results show that the groove control technique has little effect on the pump performance, the flow field and the pressure fluctuations under the design conditions. When the flow rate decreases to the saddle area, the axial velocity in the impeller inlet decreases and the velocity circulation increases. The backflow region is extended with a large scale, which causes blockage of the inlet and low frequency pressure fluctuations. The groove control technique can effectively suppress the backflow vortices, increase the flow velocity uniformity and decrease the amplitudes of pressure fluctuations, resulting in an efficient improvement for the hydraulic characteristic of a shaft tubular pump in the saddle zone working condition.