The　numerical　simulation　method　to　study　rock　breaking　process　and　mechanism　under　high　pressure　water　jet　was　developed　with　the　continuous　mechanics　and　the　FEM　theory.　The　rock　damage　model　and　the　damage-coupling　model　suited　to　analyze　the　whole　process　of　water　jet　breaking　rock　were　established　with　continuum　damage　mechanics　and　micro.　damage　mechanics.　The　numerical　results　show　the　dynamic　response　of　rock　under　water　jet　and　the　evolvement　of　hydrodynamic　characteristic　of　jet　during　rock　breaking　is　close　to　reality,　and　indicates　that　the　body　of　rock　damage　and　breakage　under　the　general　continual　jet　occurs　within　several　milliseconds,　the　main　damage　form　is　tensile　damage　caused　by　rock　unload　and　jet　impact,　and　the　evolvement　of　rock　damage　shows　a　step-change　trend.　On　the　whole,　the　numerical　results　can　agree　with　experimental　conclusions,　which　manifest　that　the　analytical　method　is　feasible　and　can　be　applied　to　guide　the　research　and　application　of　jet　breaking　rock　theory.