This　paper　explores　the　influence　of　the　confining　stress　on　rock　fragmentation　under　the　cutter　of　tunnel　boring　machine　(TBM)　by　indentation　test.　Acoustic　emission　(AE)　system　was　employed　for　real-time　monitoring　the　rock　fragmentation　process　during　the　indentation　test.　Granite　and　marble　samples　were　used　in　the　indentation　test.　The　rock　fragmentation　processes　with　the　different　confining　stress　levels　was　studied　based　on　the　characteristics　of　force-penetration　depth　curve　and　the　AE　parameters,　including　AE　energy　rare,　hit　counts,　amplitude　and　location　of　AE　events.　After　the　indentation　test,　the　rock　samples　were　cut　along　the　centerline　of　rock　samples　and　subsequently　the　crack　distribution　and　the　size　of　crushed　zone　were　measured.　The　test　results　showed　that　the　force　for　crack　initiation　and　crushed　zone　size　increased　with　increasing　confining　stress.　The　cracks　tend　to　propagate　to　the　free　surface　as　the　confining　stress　increases.　But　for　the　marble　samples,　there　exists　a　critical　confining　stress　condition,　such　that　if　the　confining　stress　is　more　than　the　critical　value,　the　force　for　crack　initiation　and　crushed　zone　size　decrease　dramatically.　Moreover,　it　was　found　that　rock　slabbing　induced　by　confining　stress　had　occurred　before　TBM　cutter　indentation.　Such　confining　stress　condition　promotes　rock　fragmentation.　(C)　2014　Elsevier　Ltd.　All　rights　reserved.