The impact erosion of particle in abrasive waterjet has the features of short duration of time and small scale of the deformation area, which lead to difficulty on implementing comprehensive investigation. As a meshless method, smoothed particle hydrodynamics is appropriate for dealing with high strain rate and large deformation issues such as impact dynamics. In this work, the erosive wear of aluminum nitride target material induced by incident particle in ultrasonic-assisted abrasive waterjet machining was investigated through establishing a 3D hybrid smoothed particle hydrodynamics-finite elements model. The results indicated that the parameters such as particle shape, impact angle, and impact velocity have remarkable effects on the erosion mechanism. The ultrasonic vibration influences the dynamic process of particle penetration and the deformation of eroded target material. Multi-impacts were also simulated and the results indicated that the erosion was influenced by the overlapping condition and ultrasonic vibration. The numerical results were verified by the experiments utilizing the specially developed setup.