In　order　to　understand　the　mechanical　characteristics　of　tree　roots　and　their　mechanical　effects　on　slopes,　the　landslide　in　Wuping　high　vegetation　coverage　area　of　Fujian　province　was　selected　as　the　research　site,　and　the　root　tensile　mechanical　properties　of　typical　tree　roots　in　the　study　area　were　tested　after　classification　by　diameter　class.　Furthermore,　in-situ　direct　shear　tests　of　root-soil　composites　under　different　root　cross-sectional　area　ratios　(RAR)　and　moisture　content　were　conducted　at　the　landslide　site,　and　investigations　were　made　into　the　distribution　characteristics　of　roots　in　the　profile　to　explore　the　mechanical　effects　of　roots　on　shallow　landslides.　The　results　showed　as　follows:　(1)　The　tensile　force　of　Pinus　massoniana　and　Cunninghamia　lanceolata　ranged　from　12.45-673.09　N　in　1-7　diameter　class,　and　the　tensile　force　was　positively　correlated　with　the　root　diameter　by　power　function;　The　tensile　strength　ranges　from　7.16　MPa　to　60.95　MPa,　and　the　tensile　strength　is　negatively　correlated　with　the　root　diameter　as　a　power　function.　The　average　tensile　force　and　tensile　strength　of　Cunninghamia　lanceolata　root　were　higher　than　those　of　Pinus　massoniana.　(2)　Tree　roots　significantly　improved　the　shear　strength　of　soil,　and　the　additional　cohesion　provided　by　roots　to　soil　was　significantly　positively　correlated　with　the　shear　plane　RAR.　The　root　structure　of　Cunninghamia　lanceolata　is　closer　to　R　type,　and　that　of　Pinus　massoniana　is　VH　type.　Under　similar　RAR,　Cunninghamia　lanceolata　roots　has　a　better　reinforcing　effect　on　the　soil　than　Pinus　massoniana.　(3)　With　the　increase　in　moisture　content,　the　shear　strength　of　the　root-soil　composites　of　Pinus　massoniana　and　Cunninghamia　lanceolata　significantly　decreases,　as　water　infiltration　diminishes　the　additional　cohesion　provided　by　the　root　systems　to　the　soil.　(4)　Based　on　the　Wu　model,　considering　the　influence　of　moisture　content　on　soil　cohesion　and　additional　root　cohesion,　an　estimation　model　for　the　shear　strength　value　of　root-soil　composites　considering　moisture　content　was　established.　Upon　verification,　the　accuracy　of　this　model　proved　to　be　higher　than　that　of　the　Wu　model,　and　the　results　were　reasonable.　(5)　Although　the　root　system　has　a　reinforcement　effect　on　shallow　landslides,　its　contribution　to　the　stability　of　shallow　landslides　under　heavy　rainfall　is　limited　due　to　the　influence　of　root　distribution　depth,　density　and　water　infiltration.