To discover the characteristic of tip clearance flow, the large eddy simulation (LES) method with sliding mesh technique was used for analyzing the unsteady flow in a low-specific-speed axial-flow pump under five different operating conditions. The tip-leakage vortices and pressure pulsations of near-tip zone on the blades were examined. It was found that the dominant tip-leakage vortex extended to the pressure side of the neighboring blade for all five investigated flow rates. As the flow rate increased from 0.7Qd to 1.2Qd, the angle between the dominant tip-leakage vortex and the blade reduced from 20°to 14°. The results also showed that the amplitude of pressure fluctuation in the near-tip zone on the blades became higher when the flow rate was farer from the design flow rate, especially on the pressure side of the blade. At the 0.7Qd condition, the pressure fluctuation amplitude of the monitoring point PP3 (at the near-tip zone on the pressure side of the blade close to the blade leading edge) was 8.5 times of the one at design flow rate, and the high-frequency pulsation occurred due to tip-leakage vortices. When the flow rate was more than 1.0Qd, the pressure fluctuations of PP3 was dominated by the rotation frequency.