The evolvement of rock fracture is a complicated and nonlinear dynamic problem. On the assumption that rock is homogeneous and isotropic, a numerical model was developed to simulate rock fracture under high pressure water jet based on continuum damage mechanics and nonlinear finite element method. The dynamic effect of rock was simulated by the dynamic contact method under high pressure water jet. The numerical simulation results showed that rock failure occurred within several milliseconds and the evolvement of it was for step under high pressure water jet and that the stress propagation in rock rapidly decayed with the distance from the jet centre. On the whole, the numerical results clearly exhibited the process of rock fracture and the extent of the water jet under high pressure water jet. It was important to the application of jet cutting rock theory and the development of water jet technology.