The　advance　rate　of　a　tunnel　boring　machine　(TBM)　excavating　in　high-strength　rock　masses　is　limited.　Creating　kerfs　on　the　working　face　using　pure　high-pressure　water　jets　(HPWJ)　is　a　feasible　way　to　improve　TBM　performance.　However,　the　influence　of　the　cracks　created　by　HPWJ　on　the　subsequent　cutter　indentation　has　not　been　investigated.　To　get　a　comprehensive　understanding　of　the　rock　breakage　mechanism　within　the　TBM　cutter　indentation　assisted　with　HPWJ,　a　full　factorial　granite　kerfing　experiment　was　conducted,　the　depth　and　width　of　the　kerfs　produced　by　HPWJ　with　various　jet　pressures　and　nozzle　traverse　speeds　were　measured.　Indentation　tests　including　different　cutter　indentation　positions　and　various　shapes　of　kerfs　created　by　HPWJ　were　performed,　the　indentation　force　and　acoustic　emission　rate　were　continuously　monitored.　Finally,　typical　kerfing　samples　and　indentation　samples　were　sectioned　to　observe　the　internal　rock　fracture　pattern　using　fluorescent　dye.　The　kerfing　test　results　indicated　the　granite　kerfing　mechanism　by　HPWJ　consisted　of　the　grain　erosion　and　the　dynamic　impingement.　A　new　index　of　unit　loading　energy　(Eu)　of　HPWJ　was　proposed,　which　was　the　energy　input　into　the　rock　as　the　jet　traversed　a　unit　distance　of　the　nozzle　diameter.　The　influence　of　Eu　on　the　kerf　shape　and　inner　cracks　pattern　was　analyzed.　The　indentation　test　results　indicated　a　shallow　wide　kerf　with　less　cracks　produced　by　HPWJ　using　a　low　Eu　could　drastically　reduce　the　high　indentation　force　if　the　cutter　loaded　on　the　kerf.　However,　a　deep　narrow　kerf　with　long　inner　cracks　created　by　HPWJ　using　a　high　Eu　could　facilitate　the　crack　expansion　during　the　cutter　indentation　if　the　kerf　was　arranged　on　the　side　of　the　cutter.　In　this　case,　a　critical　spacing　between　the　kerf　and　cutter　existed,　below　which　the　rock　chip　could　be　created　with　the　lower　indentation　force,　and　the　critical　spacing　increased　with　the　increasing　Eu.　This　study　is　conducive　to　a　rational　cutterhead　design　of　TBM　assisted　by　HPWJ.　©　The　Author(s),　under　exclusive　licence　to　Springer-Verlag　GmbH　Austria,　part　of　Springer　Nature　2024.