Modified　suction　caissons　(MSCs)　acting　as　offshore　wind　turbine　foundations　will　generate　the　accumulated　rotation　under　cyclic　loading　resulted　from　waves.　The　accumulated　rotation　and　the　range　of　soil　deformation　around　the　MSC　under　long-term　cyclic　wave　loading　were　studied　using　3-D　numerical　simulations.　The　Morison　equation　was　adopted　to　calculate　the　wave　loadings.　It　was　found　that　the　MSC　accumulated　rotation　increases　linearly　with　the　increase　of　the　logarithm　of　cyclic　number.　The　normalized　expression　was　proposed　to　reflect　the　relationship　between　the　accumulated　rotation　and　cyclic　number.　The　soil　deformation　range　around　the　MSC　increases　when　increasing　the　cyclic　number　and　loading　amplitude.　It　can　also　be　concluded　that　the　accumulated　rotation　increases　rapidly　with　this　change　of　excess　pore　pressure　in　the　first　4000　cycles.　The　responses　of　the　MSC　to　wave　and　wind　loads　were　also　investigated.　Results　show　that　the　accumulated　rotation　of　the　MSC　under　both　wave　and　wind　loadings　is　larger　than　that　under　the　wave　loading　only.　©　2020,　Chinese　Ocean　Engineering　Society　and　Springer-Verlag　GmbH　Germany,　part　of　Springer　Nature.