The　systems　of　offshore　wind　turbines　are　established　in　a　complex　marine　environment,　and　are　subjected　to　all　kinds　of　ocean　loadings　such　as　waves,　currents　and　wind　for　a　long　time.　It　is　found　that　offshore　wind　turbine　foundations　are　seldom　damaged　due　to　the　problem　of　strength　and　stability　under　normal　operation　conditions.　Most　of　the　damages　are　caused　by　the　fatigue　damage　under　long-term　loads.　Aimed　to　this　problem,　the　monopile　foundation　of　offshore　wind　turbine　is　analyzed　as　an　example　in　this　study.　The　fatigue　damage　is　analyzed　systematically　using　the　method　of　time-domain,　combining　the　rain-flow　counting　method,　S-N　curve　with　linear　and　nonlinear　fatigue　damage　models.　In　addition,　a　modified　nonlinear　fatigue　damage　model　is　proposed　based　on　the　Corten-Dolan　and　Manson-Halford　nonlinear　fatigue　damage　models,　which　can　consider　the　modification　of　load　interactions　and　the　effect　of　loading　sequence.　In　this　way,　the　short-term　fatigue　damage　value　of　offshore　wind　turbine　foundation　can　be　obtained.　On　the　basis,　the　long-term　probability　distribution　function　of　wind　speed　is　obtained　according　to　the　actual　monitoring　results　of　wind　load,　and　the　fatigue　damage　value　of　the　offshore　wind　turbine　foundation　in　the　design　life　can　be　obtained.　Finally,　a　complete　fatigue　damage　analysis　method　of　offshore　wind　turbines　is　proposed,　which　is　applicable　to　both　short-term　fatigue　damage　and　long-term　fatigue　damage.