The abrasive water jet has remarkable effect in the application of accelerating drilling speed, deep penetration perforation and fracturing stimulation. In-depth understanding of the mechanism of abrasive water jet rock breaking is one of the keys to improve its application effect. Based on the arbitrary Lagrange-Euler finite element coupling algorithm, an independent packaged finite element mesh method for describing abrasives is presented in this paper. The grid of the water jet unit is set to change with the movement of the material to realize the fluid flow characteristics, and the speed is set to the material. The abrasive unit is set to the grid does not change with the movement of the material to achieve the solid particle characteristics, and the speed is set to the grid. Considering the dynamic impact damage of rock and the cooperation between water jet and abrasive, an abrasive water jet rock breaking model was established to characterize the multi-phase and multi-physical coupling process of water jet flow, rock damage and failure. The model focused on the impact damage of abrasive particles and water jet on rock in microseconds. Two sets of meshes were used to capture the collaborative rock breaking action of abrasives and water jets, and the temporal and spatial evolution characteristics of key parameters such as rock breaking volume, rock damage field, pressure field of water jet and energy contribution rate of water jet and abrasive to rock breaking were obtained. The results show that abrasive plays the main role and water jet plays the auxiliary role in the process of rock breaking. The mechanism of abrasive and water jet cooperative rock breaking is analyzed. The abrasive impingement of rock causes high degree of local damage of rock, which reduces the difficulty of water jet breaking rock. In addition, the impact of abrasive water jet on rock breakage creates a new interface between water jet and rock, which increases the impact pressure water jet and improves the rock breaking ability of water jet. Therefore, water in abrasive water jet has higher impact force and energy utilization rate than that of pure water jet. The predamage of abrasive impact on rock combined with the higher pressure of water jet stagnation is one of the important mechanisms that abrasive water jet has several times higher efficiency and energy utilization than pure water jet. The results can provide a theoretical model and design basis for optimizing the rock breaking parameters of abrasive water jet.