How to achieve the most efficient rock-breaking is the research direction of the rock-breaking technique. According to this problem, a series of experiments relating to the rock-breaking efficiency of cavitating water jets were carried out for different nozzles within different pump pressures and ambient pressures. The results show that the erosion depth increases proportionally with the pump pressure and decreases as the ambient pressure increasing on the same experimental condition. Erosion happens in the first few minutes, and after that, erosion does not increase with time. The erosiondepth of the convergent-straight nozzle is much lower than that of the convergent-divergent nozzle.