To　evaluate　the　stability　of　the　large-diameter　cylindrical　structure　in　soft　ground　under　wave　loading,　considering　the　cyclic　softening　effect　of　soft　clay　induced　by　wave　loading,　a　nonlinear　elasto-plastic　constitutive　model　based　on　the　concept　of　cyclic　shear　strength　of　clay　is　proposed　and　numerically　implemented　in　the　FEM　software　ABAQUS.　In　the　model,　the　concept　of　cyclic　strength　is　combined　with　the　Duncan-Chang　nonlinear　strain-stress　relationship　under　undrained　condition.　Then　a　series　of　three　dimensional　finite　element　numerical　analyses　are　conducted　to　explore　the　cyclic　capacity　and　failure　mechanisms　of　large-diameter　cylindrical　structure　in　soft　ground.　The　computed　results　are　compared　with　those　obtained　under　monotonic　loading　without　considering　the　cyclic　softening　effect.　The　results　indicate　that　the　failure　mode　of　cyclic　instability　and　distribution　of　equivalent　plastic　strain　in　soft　ground　is　somewhat　different　from　those　of　ultimate　failure　state.　Parametric　studies　show　that　the　bearing　capacity　is　reduced　considerably　due　to　the　cyclic　softening　effect　induced　by　wave　loading　with　respect　to　ultimate　bearing　capacity　and　is　influenced　by　some　factors　such　as　the　embedment,　height　of　load　action　point　and　cyclic　loading　number　to　failure　etc.