In order to clarify the cavitation near the clearance outlet, firstly, the detailed dependence checks were done to ensure the calculation accuracy. Based on these, the unsteady calculations including cavitation were done and the cavitation near the clearance outlet under NPSHr condition was predicted. Results showed that the static pressure presented a periodical non-uniform distribution with frequency of 2.27 times of the rotation frequency due to the rotation effects near the wear-ring. The cavitation occurred at the low-pressure region which located at the circle whose center was the center of the inlet pipe and the radius was slightly smaller than the intersection radius of the inlet pipe and the wear-ring outlet. The pressure pulsation near the wear-ring outlet was influenced by the impeller rotation and cavitation, it had two kinds of frequency, the first one was the blade passing frequency and it’s multiple, the second one was caused due to the periodic changes of cavitation and the frequency was an integral multiple of cavitation frequency. The conclusion was helpful to get a better understanding of the cavitation characteristics in the centrifugal pump near the wear-ring clearance.