To explore the relationship among the erosion ability of high-pressure cavitating water jets, hydraulic parameters and rock nature with a series of experiments relating to the efficiency of rock-breaking with cavitating water jets for different porosity of rock under different confining pressures and pump pressures. The results show that the erosion efficiency (erosion mass and erosion depth) of cavitating water jets is fitted a conic curve with pump pressure and confining pressure. It increases with the pump pressure increases while decreases with the confining pressure increases; the length of the bubble cloud decreases with the confining pressure increase and the length increases with the pump pressure increase, which is accorded with cubic curve. The bubble cloud length influences the rock-breaking efficiency by deciding the valid stand-off distance directly. Under the experimental condition, the cavitation happens once the pump pressure reaches 7MPa, and the cavitating water jets can crushing the sandstones which the uniaxial compressive strength is 96MPa. On the other hand, the porosity of rock is another main factor of rock breakage with high pressure cavitating water jets. The higher the porosity of rock is, the easier the rock can be broken.