Many　offshore　wind　farms　have　already　been　constructed　and　more　are　planned　in　China.　Monopiles　with　pile　diameter　more　than　1.5　m　are　the　main　foundation　form　of　wind　turbine　generators.　The　determination　of　the　axial　pile　capacity　(especially　shaft　resistance)　of　monopiles　is　one　of　the　important　issues　for　offshore　structures.　A　series　of　full-scale　offshore　static　load　tests　of　openended　steel　pipe　piles　are　conducted　at　two　thick　overburden-layer　sites.　The　load-settlement　curve　at　pile　head,　axial　force　and　inner　and　outer　friction-resistance　ratio　(friction-resistance　ratio)　along　the　pile　shaft　are　derived.　The　results　show　that　the　inner　shaft　friction　is　indispensable　for　large-diameter　open-ended　steel　pipe　piles,　and　the　piles　are　approximately　full　cored.　At　the　upper　3　m　close　to　the　ground　surface,　the　friction-resistance　ratio　is　relatively　small,　and　the　average　value　is　about　0.15.　An　increasing　trend　with　depth　is　obvious.　At　the　critical　depth　region,　the　average　ratio　in　the　cohesive　soil　and　cohesionless　soil　varies　from　0.28　to　0.43　and　0.26　to　0.40,　respectively.　Furthermore,　the　ratio　continues　to　increase　as　it　goes　deeper,　and　the　maximum　ratio　is　no　more　than　0.5.　A　new　design　method　considering　the　influence　of　pile　diameter　and　embedded　depth　is　employed　to　calculate　the　inner　and　outer　friction-resistance　ratio.　The　performance　of　the　new　design　method　is　assessed　against　the　field　test　results.　©　2020,　Taiwan　Geotechnical　Society.