Abstract: To consider reasonably the cyclic softening effect with strength degradation of soft clay，a nonlinear elasto-plastic model based on the concept of cyclic shear strength of clay was proposed. In the model，the concept of cyclic strength was combined with the Duncan-Chang nonlinear elastic relationship and Mises yield criterion under undrained condition. Then a series of finite element analysis were conducted to explore the stability and cyclic and static coupling effect of skirted foundations in soft ground. The results computed were verified through comparing with the available model test under monotonic loading. The results indicated that the peak cyclic load was reduced considerably with respect to ultimate bearing capacity. Parametric studies showed that the peak cyclic load without considering the nonlinear elastic relationship was higher than that reflecting the effect. When the static vertical load level was smaller，the instability of foundation was caused mainly by cyclic load，whereas the level was larger，the failure of foundations was due to static load.