It　was　discovered　in　tests　that　the　increase　in　effective　confining　pressure　could　have　a　great　impact　on　the　mechanical　behavior　of　hydrate-bearing　sediment,　which　was　not　only　decreased　the　internal　friction　angle　and　dilatancy,　but　also　enhanced　cohesion　and　strength.　Significant　crushing　of　the　hydrate-host　sand　was　founded　after　shearing　under　high　pressure.　In　this　study,　a　discrete　element　method　(DEM)　model　considering　the　effects　of　particle　breakage　and　hydrate　repolymerization　was　proposed,　and　a　series　of　numerical　triaxial　tests　were　performed　to　shed　light　on　the　mechanism　of　mechanical　properties　evolution　observed　in　the　physical　tests.　The　numerical　results　revealed　that　the　breakage　of　host　particles　was　a　leading　cause　of　the　decrease　in　the　internal　friction　angle　and　transformation　from　shear　dilation　to　contraction.　As　the　hydrate　saturation,　axial　strain,　and　effective　confining　pressure　increased,　the　force　chain　network　of　the　model　became　denser　and　the　force　magnitude　on　the　chains　became　increasingly　uniform,　which　leads　to　the　increase　in　model　strength;　the　number　and　force　of　bonded　contact　also　increased　gradually,　resulting　in　increased　cohesion　on　the　macro　scale.　©　2022　Elsevier　Ltd