Abstract: In order to improve the cavitation characteristics of the flflow fifield on the suction side of the hydrofoil under high-speed flflow conditions, a method of active water jet arranged on the suction side is proposed to control the flflow around the hydrofoil. Based on a fifilter-based density correction turbulence model combined with Zwart-Gerber-Belamri cavitation model, the inflfluence of the water jet on the cavitation and hydrodynamic characteristics of the hydrofoil is analyzed when the cavitation number is 0.83, the angle of attack is 8◦ and the water jet is 0.19c from the foil leading edge. The intensity of the re-entrant jet is analyzed quantitatively to explore the relationship between the re-entrant jet and the cavitation characteristics of the flflow fifield. The numerical results show that the time-average cavity volume on the suction side of the hydrofoil with jet is 14/15 smaller than that of the original hydrofoil, which indicate that the water jet can signifificantly weaken the development of cavitation, and thus the cavitation pattern in the flflow fifield transforms from cloud cavitation to sheet cavitation. Moreover, the water injection greatly improves the hydrodynamic performance of the hydrofoil. The lift to drag ratio of the hydrofoil increases by 22.9% compared with that of the original hydrofoil, meanwhile, and the shedding frequency of the cavitation decreases by 26.2%, and the amplitude caused by the shedding of the cavitation decreases by 9.1%. The water jet shrinks low pressure area on the suction side sharply and reduces the reverse pressure difffference of flflow in the vicinity of the hydrofoil, as a result, intensity of the re-entrant jet declined. The water injection also thins the boundary layer which enhances the anti-reverse pressure gradient capability of the flflow and then blocks the re-entrant jet. Those explain the mechanism of cavitation flflow control by active water injection.