Landslides　are　a　typical　geological　hazard　that　can　cause　large　numbers　of　casualties　and　huge　economic　losses,　and　the　overflow　of　a　weir　from　a　blocked　river　landslide　can　have　even　more　disastrous　consequences.　Of　the　different　types　of　landslides,　about　33%　of　landslides　happen　in　anti-dip　slopes.　This　paper　reports　a　massive　ancient　anti-dip　river-damming　landslide　on　the　Jinsha　River:　the　Zongrongcun　landslide.　Field　investigation　and　theoretical　analysis　were　used　to　reveal　the　potential　mechanism　of　this　ancient　landslide,　and　the　block　discrete　element　software　3DEC　was　used　to　replicate　its　landslide　process.　The　findings　from　the　present　study　are　as　follows:　(1)　blocks　in　this　landslide　were　classified　into　significant　slide,　significant　toppling,　and　significant　slide　categories　based　on　D-f.　(2)　The　whole　landslide　was　divided　into　significant　sliding　and　toppling　zones　by　D-f　=　0.5.　(3)　The　results　show　that　the　river-damming　landslide　was　likely　to　be　triggered　by　river　erosion,　heavy　rainfall,　gravity.　Under　strong　valley　trenching,　the　rocks　on　the　slope　fractured　under　gravity　and　tectonic　stress.　These　factors　caused　rock　blocks　tensile　fracture　failure.　Then　a　penetrating　sliding　surface　formed　on　the　slope,　which　subsequently　caused　this　river-damming　landslide.