The　instability　of　jointed　rock　mass　is　usually　the　shear　process　of　the　rock　mass　along　discontinuities　under　the　influence　of　groundwater　flow.　By　conducting　laboratory　tests　and　numerical　experiments　on　the　shear-flow　coupling　of　rock　joints　under　constant　normal　stiffness　(CNS)　and　constant　normal　stress　(CNL)　boundary　conditions,　the　influence　of　normal　boundary　conditions　and　seepage　pressure　on　the　shear　mechanical　and　flow　characteristics　of　joints　were　investigated.　The　test　results　were　as　follows:　The　joint　shear　stiffness,　peak,　and　residual　shear　strength　under　the　CNS　boundary　condition　were　predominantly　larger　than　those　under　the　CNL　boundary　condition.　Overall,　these　parameters　were　positively　correlated　with　the　initial　normal　stress　sigma(n0).　When　sigma(n0)＞　2　MPa,　the　postpeak　shear　stress　of　the　CNS　boundary　condition　showed　a　sharp　decrease,　whereas　that　of　the　CNL　boundary　condition　changed　from　a　slowly　decreasing　type　(sigma(n0)=4　MPa,　6　MPa)　to　a　sharply　decreasing　type　at　sigma(n0)=8　MPa.　The　peak　dilation　rate　under　the　CNS　boundary　condition　at　all　levels　of　normal　stress　was　lower　than　that　of　CNL,　and　the　strain　softening　in　postpeak　of　the　latter　was　more　remarkable.　In　the　process　of　joint　shear,　the　hydraulic　aperture　displayed　a　four-stage　variation　law　of　＂steady-sudden　increase-slow　increase-basically　stable.　＂　Moreover,　the　hydraulic　aperture　under　the　CNS　boundary　condition　was　always　lower　than　that　under　the　CNL　boundary　condition.　The　seepage　pressure　increased　from　0.5　MPa　to　1.5　MPa,　and　the　average　hydraulic　aperture　in　the　stable　stage　under　normal　stress　at　all　levels　increased　from　0.146　mm　to　0.187　mm.　In　addition,　the　average　peak　shear　stress　and　average　shear　stiffness　decreased　by　0.9　MPa　and　0.83　GPa/m,　respectively.　We　also　established　a　numerical　model　of　a　real　rough　three-dimensional　joint,　compiled　a　calculation　program　for　the　shear-flow　process　of　a　joint　under　CNS　boundary　conditions,　and　visualized　the　flow　channel　inside　the　joint.　The　seepage　flow　bypassed　the　area　where　the　joints　contacted　each　other,　forming　obvious　flow　channels.　The　flow　rate　increased　at　the　intersection　of　the　flow　channels.