Disc　cutter　wear　is　one　of　the　comprehensive　results　of　the　rock-machine　interaction　in　tunnel　boring　machine　(TBM)　tunneling.　The　replacement　of　the　disc　cutter　is　a　time-consuming　and　costly　activity　that　can　significantly　reduce　the　TBM　utilization　(U)　and　advance　rate　(AR),　and　has　a　major　effect　on　the　total　time　and　cost　of　TBM　tunneling　projects.　Therefore,　the　importance　of　predicting　the　cutter　life　accurately　can　never　be　overemphasized.　Most　cutter　wear　prediction　models　are　only　suitable　for　17-in.　or　smaller　disc　cutters.　However,　use　of　large-diameter　disc　cutters　has　been　an　irresistible　trend　for　large-section　hard　rock　TBMs.　This　study　attempts　to　reveal　the　genuine　wear　rule　of　a　20-in.　disc　cutter　and　develop　a　new　empirical　model　for　predicting　the　cutter　life　in　granite　based　on　field　data　collected　from　a　water　conveyance　tunnel　constructed　by　the　TBM　tunneling　method　in　China.　The　field　data　including　the　actual　cutter　wear　and　the　geological　parameters　along　the　studied　tunnel　were　compiled　in　a　special　database　that　was　subjected　to　statistical　analysis　to　reveal　the　genuine　wear　rule　of　a　20-in.　disc　cutter　and　develop　the　reasonable　correlations　between　some　common　intact　rock　parameters　and　the　disc　cutter　life.　These　equations　were　developed　based　on　data　from　massive　to　very　massive　granite　with　a　UCS　range　of　40-100　MPa,　which　can　be　applied　for　the　assessment　of　the　cutter　life　of　a　20-in.　disc　cutter　in　similar　hard　rock　projects　with　similar　rock　strengths　and　rock　abrasivities.