In　order　to　study　the　specimen　size　effect　and　engineering　characteristics　of　soils　under　marine　geological　conditions,　K0　consolidated-undrained　triaxial　tests　with　different　specimen　dimensions　were　performed　on　strongly　weathered　granite　of　a　seabed　of　Pingtan　island,　Fujian　Province.　Differencs　of　the　stress-strain　behavior,　critical　state　line,　shear　strength　indexes　and　particle　breakage　between　specimens　at　different　sizes　were　studied,　and　the　specimen　size　effect　was　discussed.　The　results　show　that　the　stress-strain　relationship　of　specimens　with　different　sizes　is　similar.　The　slope　of　critical　state　line　of　smaller　specimen　is　less　than　that　of　larger　specimen.　The　shear　strength　indexes　decrease　with　the　increase　of　specimen　size.　The　particle　breakage　rate　increases　with　the　increase　of　specimen　size.　Specimen　size　effect　in　engineering　practice　should　be　paid　attention.　©　2020,　Central　South　University　Press.　All　right　reserved.