In　marine　environment,　the　monopile　offshore　wind　turbines　(MOWTs)　are　subjected　to　long-term　horizontal　cyclic　loads　caused　by　wind,　waves　and　currents,　which　will　lead　to　the　stiffness　degradation　and　plastic　cumulative　deformation　of　clays.　The　decrease　of　clays　bearing　capacity　caused　by　long-term　cyclic　degradation　effect　is　a　threat　to　the　safe　use　of　MOWTs　in　earthquake-prone　countries　(such　as　some　countries　in　the　circumPacific　seismic　belt).　A　three-dimensional　finite　element　model　is　established　to　research　the　seismic　response　analysis　of　MOWT　in　clays　considering　the　long-term　cyclic　degradation　effect.　The　cumulative　deformation　of　pile-soil　system　after　long-term　cycle　are　obtained　by　adopting　the　stiffness　degradation　of　clays　through　the　USDFLD　subroutine.　On　this　basis,　the　dynamic　response　analysis　of　MOWT　system　under　the　combined　action　of　seismic　and　environmental　loads　is　carried　out.　The　influence　of　long-term　horizontal　cyclic　load　number,　longterm　horizontal　cyclic　load　amplitude,　seismic　intensity,　soil　strength,　environmental　loads　and　cyclic　degradation　parameter　on　the　dynamic　response　of　MOWT　is　analyzed.　In　the　seismic　design　of　MOWTs,　the　effects　of　long-term　degradation　and　random　wind,　waves　and　other　environmental　loads　should　be　considered.