The　tunnel　boring　machine(TBM)　performance　is　influenced　by　the　joint　spacing　in　a　large　extent.　TBM　penetration　rate　increases　with　decreasing　joint　spacing.　But,　too　small　joint　spacing　makes　the　tunnel　face　in　stable　that　is　not　favorable　to　TBM　excavation.　The　rock　masses　along　the　headrace　tunnel　of　Jinping　II　hydropower　station　are　composed　of　marble　with　different　thicknesses　of　the　layers.　The　thickness　varies　largely　along　the　tunnel　alignment　from　several　centimeters　to　several　meters.　The　layer　surface　is　the　main　non-continuous　face　in　these　rock　masses　and　the　intersection　angle　between　the　tunnel　axis　and　the　layer　is　from　60°　to　80°.　The　rock　breakage　process　in　the　tunnel　is　influenced　by　the　high　in-situ　stress　and　the　layer　thickness.　TBM　performance　is　analyzed　in　thin　layer,　thin　to　middle　layers　and　thick　layer　marble　rock　masses　under　the　high　in-situ　stress　from　the　point　view　of　rock　breakage　mechanism　by　TBM,　respectively.　The　influence　of　the　layer　thickness　on　TBM　penetration　is　studied.