It was summarized for the length of cavitation cloud versus different nozzles with different pump pressures and ambient pressures based on the forming process of cavitation cloud. It is pointed out that the length of cavitation cloud increases with pump pressures

while there has a best one with ambient pressures. The difference of erosion characteristic between converging-diverging nozzle and converging nozzle was analysed by experiment; and it is shown that the capability of average mass rock-erosion by cavitating water jet with converging-diverging nozzle are 7 times than converging nozzle in the same bump pressure. In contrast

it is shown that the depth and the diameter of erosion as well as mass erosion decrease with the increasing of ambient pressure; so that the influence on rock-erosion capability with converging-diverging nozzle in ambient pressure is disadvantageous.