Although　the　root　can　enhance　the　soil＇s　strength,　vegetation　cover　landslide　still　occurs　frequently　under　the　rainfall.　To　elucidate　the　mechanism　underlying　the　degradation　of　the　shear　strength　of　root-soil　composites　under　the　influence　of　moisture,　we　investigated　trees　from　hilly　slopes　in　southeastern　China.　The　tensile　mechanical　properties　of　roots　were　tested　under　varying　moisture　conditions.The　results　of　previous　work　on　the　friction　characteristics　of　the　root-soil　interface　under　different　soil　water　content　were　also　considered.　Furthermore,　large-scale　direct　shear　tests　were　performed　to　assess　the　strength　characteristics　of　root-soil　composites　under　different　root　cross-sectional　area　ratios　(RAR)　and　moisture　contents.　Based　on　the　widely　used　Wu　model,　and　incorporating　the　failure　modes　of　roots　in　root-soil　composites　and　the　mechanism　of　root-soil　interface　friction,　a　root-soil　composite　strength　degradation　model　was　established　considering　the　effects　of　moisture.　Moisture　significantly　affected　the　tensile　strength　of　fine　tree　roots,　with　the　tensile　strength　of　fine　roots　being　lower　in　the　saturated　state　than　in　the　fresh　state.　In　contrast,　coarse　roots　were　almost　unaffected　by　moisture.　As　the　moisture　content　increased,　the　additional　strength　provided　by　the　roots　decreased,　and　the　root　efficiency　(REp)　decreased　significantly.　The　model　was　validated　against　experimental　data,　and　the　calculated　results　were　accurate.　In　root-soil　composites,　as　moisture　infiltrates,　the　tensile　strength　of　the　roots,　soil　shear　strength,　and　root-soil　interface　shear　strength　decrease　to　different　degrees.　This　results　in　reduced　resistance　to　deformation　in　the　root-soil　composites,　leading　to　a　decrease　in　its　strength.