Abstract: The pressurized pulsed water jet has certain application potential in assisting disc cutters to crush hard rock because of its good damage effect on hard rock. In order to further reveal the failure mechanism of pressurized pulsed water jet (PPWJ) impacting granite under two typical working conditions(conditionⅠ: the booster chamber has an initial pressure; conditionⅡ: There is no initial pressure in the booster chamber), and to clarify the influence trends of key parameters such as initial pressure, driving pressure, target distance and impact time on the rock breaking results of PPWJ, PPWJ impacting granite under two typical working conditions were carried out, and the rock breaking results were analyzed by CT(Computed Tomography) scanning, three-dimensional reconstruction and SEM(scanning electron microscope). The research results show that: Under conditionⅠ, the main impact damage of PPWJ to granite is “hole”. The axial shear impact of the jet causes initial “hole” failure of granite until erosion is stopped. A very small part of the jet passes through the primary micro-cracks around the “hole” and causes small-scale water wedge expansion and fracture failure. At this time, PPWJ’s main impact on rock mass is transgranular; Under conditionⅡ, the impact damage of PPWJ on granite is mainly caused by “craters”. The tensile stress wave generated when the tip of the jet pulse impacts on granite produces tensile micro-cracks in the rock body. The initial “hole” generated by the axial shearing action of the jet enters the tensile micro-cracks, and the fluid expands to the crystalline weak surface by relying on the water wedge tension. At this time, PPWJ’s impact on the rock mass is mainly intergranular and transgranular; The initial pressure is the distinguishing point between two typical working conditions. conditionⅡ has better damage effect on granite without initial pressure; With the increase of driving pressure, the damage effect of granite gradually increases, but the gain is limited; PPWJ has caused considerable damage to the rock mass at the impact time of 60 seconds; The optimal dimensionless impact target distance of PPWJ is about 400, which is much larger than that of conventional water jet; The comprehensive damage ability of PPWJ to granite under conditionⅡ is much greater than that under conditionⅠ. The research results provide a solution for the efficient crushing of hard rock.