Abstract: Tip leakage vortex cavitation in a scale-model of axial flow pump model at design conditions was simulated using a modified SST k-ω turbulent model and a cavitation model. Numerical results were compared with the high-speed photography experimental data. The structure of a tip leakage vortex cavitation flow field was discussed and the evolution of cavitation bubble cloud was revealed at different cavitation conditions. Investigation results show that the modified numerical method in this paper could simulate the tip leakage vortex cavitation in the tip region of the impeller. The cavitation inception in an axial flow pump occurs in the tip clearance and leakage vortex regions. With cavitation number σ decreasing, the cavitation region is expanded to the rolling-up zone of the tip leakage flow. At a small cavitation number σ condition, the bubble cloud occurs in the suction sides of blades at the axial direction, which could induce flow instability and cavitation noise.