To improve the working ability of Helmholtz self-excited waterjets, LES was used in the flow of the cavity using UDF dynamic grid-driven ultrasonic focusing vibration boundary, and the reliability of the model was verified by comparing the simulated and experimental values of the outlet pressure. The study explored how external ultrasonic vibration and varying frequencies influenced self-excited frequency, velocity, and cavitation. From the perspective of energy conversion, the reason for the enhanced shear characteristics inside the chamber is revealed. The vapor phase distribution in the lower chamber under various conditions was compared, and the jet performance of each section of the jet structure was analyzed. Explained the development process of periodic vortex structures under ultrasonic excitation. The results show that when the ultrasonic excitation at 25 kHz compared to ordinary jet, the natural oscillation frequency soared 3.14-fold, main frequency and amplitude became more pronounced, though jet speed marginally decreased (1.89%). Higher excitation frequencies didn't significantly curb speed. The ultrasonic excitation bolstered energy transfer and vortex feedback, intensifying shear and raising vapor phase content (0.5 ≤ y/r₂≤ 0.81) in the outlet. The ability of self-excited oscillating cavitation waterjets can be significantly improved. The research results can provide theoretical basis for the application of Helmholtz type self oscillating jet.