Abstract: To investigate the rock-breaking effects of abrasive water jets, an experiment is conducted to test five types of hard rock samples with different strengths under the conditions of a pulsating pure water jet and a pulsating abrasive water jet. Using the size of erosion pits as a measure, we compare the rockbreaking effects of these two jets with those of a continuous pure water jet and a continuous abrasive water jet. The results indicate that in the eroding process, the continuous abrasive water jet mainly relies on the grinding action of abrasive particles, while the pulsating one combines such action with a continuous water hammer effect. In the condition of no abrasive particle in the jet flow, the erosion of a continuous water jet primarily depends on a single water hammer pulse that occurs only at the initial stage of the jet, while a pulsating one generates a sequence of pressure pulses that impact the rock samples continuously, leading to fractured zones in the rock sample.