The cavitation erosion characteristics of self-excited cavitating waterjet produced by a nozzle with various lip geometries were investigated. The cavitation erosive intensity was estimated by the mass loss of pure aluminum specimens and the sound press level of under the optimum standoff distance. The power spectrum density of noise and the surface profiles of the specimens were studied to uncover the influencing mechanism. The variables of lip geometries include: straight length (L1/d = 0.15–0.75), expansion angles (0–40°), expansion length (L2/d = 0.5–3). It is shown that the nozzle lip geometry can produce a significant influence on the cavitation erosion characteristics. The cavitation erosive ability can be affected by the straight length based on the vena contracta and pressure fluctuation feedback. The expansion structure can influence the jet’s cavitation erosive characteristic from two different aspects: the jet’s structuring frequency and the periodic behavior of the cavitation cloud. Moreover, it is possible to define an optimal geometry under this condition where the erosion mass loss is at a relative maximum, that is straight length L1/d around 0.35, expansion angle 10°<θ<25°, length 1.0<L2/d<2.5.