The　high-speed　water　jet　impact　model　of　17-4PH　(0Cr17Ni4Cu4Nb)　is　established　by　using　the　smoothed　particle　hydrodynamics　(SPH)　and　finite　element　method　(FEM)　coupling　algorithm　(SPH-FEM)　based　on　the　nonlinear　explicit　software　ANSYS　LS-DYNA.　The　grid　independence　is　verified　and　the　impact　process　between　high-speed　jet　and　target　is　simulated.　The　influences　of　jet　angle,　jet　velocity　and　surface　roughness　on　the　water　erosion　characteristics　of　the　target　material　are　systematically　studied.　The　results　show　that　under　the　same　target　surface　structure,　the　greater　the　initial　jet　angle　of　the　target　surface　is,　the　more　serious　the　water　erosion　damage　of　material　becomes.　Surface　roughness　has　a　great　influence　on　water　erosion.　The　average　mass　loss　of　the　10　μm　groove　samples　is　1.6　times　that　of　the　2　μm　groove　samples.　And　the　average　mass　loss　of　the　2　μm　groove　sample　is　approximately　1.4　times　that　of　a　smooth　surface　sample.　The　improvement　of　the　surface　smoothness　can　promote　the　free　expansion　of　the　pressure　wave　of　the　water　droplets　and　significantly　reduce　the　impact　pressure,　thereby　improve　water　erosion　resistance　of　the　material.　The　mass　loss　of　the　material　increases　with　the　increase　of　jet　velocity.　There　is　an　exponential　relationship　between　the　cumulative　water　erosion　mass　loss　of　the　target　material　and　the　jet　velocity.　Fitting　results　show　that　the　velocity　exponent　of　water　erosion　is　about　3.83.　©　2021,　Editorial　Office　of　Journal　of　Xi＇an　Jiaotong　University.　All　right　reserved.