To investigate the effect of high-pressure water jet assistance on hard rock breakage by mechanical impact, a rate-dependent constitutive model was adopted to describe the mechanical behavior of the rock. Then, a numerical model of rock breakage was developed using the coupled smoothed particle hydrodynamics (SPH) and finite element method (FEM). The indenter and rock stress and rock breakage features were used to evaluate the assisted effect of the high-pressure water jet. The rock stress perturbation by water jet assistance was more intense than that by indenter impact alone, which could result in more microscopic damage in the hard rock. For the normal indenter and water jet impact velocities, the peak indenter stress could be reduced by more than 30%. As the distance between the indenter and water jet impact points increased from 0 to 12.5 mm, the peak indenter stress decreased accordingly from 71.6% to 14.7% compared with the indenter stress without water jet assistance, and it decreased with increasing distance. The influence rule of the bilateral water jets on rock breakage and indenter stress is analogous to the unilateral condition, but the enhanced degree of breakage performance with bilateral water jets is better than that of the unilateral water jet. The inclined angle of the water jet also has an important effect on the rock breakage performance, and the indined angle in the range of 80 degrees similar to 90 degrees is better for hard rock breakage. The allowable intersection angle between the impact directions of the water jet and indenter is important and significant for retaining the structural integrity of the indenter. (C) 2020 Elsevier B.V. All rights reserved.