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Transient pulsation of tip leakage vortex is an important factor for flow instability and stall of centrifugal impeller. To get an insight into the unsteady flow characteristics in the tip region of a semi-open centrifugal pump, the SST k-ω two-equation model was used to solve the N-S equation. And the fast Fourier transform (FFT) was used to transform the time domain value of vorticity of each monitoring point into frequency domain value, so as to monitor the frequency domain characteristics. The correlation mechanism between the leakage vortex trajectory and the blade loading was studied and the spectral characteristics of the leakage vortex were analyzed. The results showed that the angle θ between the leaking vortex core and the blade bone line was changed periodically with the tip blade loading. The leakage flow accelerated the flow separation at the tip, forming a vortex tube extending from the tip blade surface to the shroud. At 0.75Qd, the 0.51fB in the tip region was the main disturbance signal, which was closely related with the secondary leakage and the unsteady pulsation of the vortex tube. As the flow rate decreased, the disturbance frequency was changed, and the tip leakage vortex crushing position was moved toward the leading edge of the blade. Under the near-stall operating points, the unsteady fluctuation of the leakage flow was aggravated by the pulsation and shedding of the vortex tube, and the tip leakage vortex crushing position was extended to the leading edge of the blade. The unsteady characteristics of the tip leakage flow of the semi-open centrifugal pump were researched, which provided a theoretical basis for the optimal design of the semi-open impeller and the capture of stall signal.