The deformation characteristics of soft foundation subjected to long-term cyclic loading is significant. Various models have been developed for predicting cumulative plastic strain in clay under repeated loading. The most commonly used is empirical model, but it has some limitations. Based on the dynamic deformation curve of typical structured clay, an improved model is proposed to describe the cumulative deformations of clay subjected to cyclic loading, by adding exponential function of to the exponential hyperbola model of . This model applies to both stable strain curve with the strain limit and destructive strain curve under different stress levels. As for brittle failure of strong structured clay, the model has obvious advantages, and it also shows good universality of dynamic deformations of different structured clays under different stress levels. What is more, the improved model can be used to calculate the critical dynamic stress approximately. Since the behavior of structured clay is damaged promptly under dynamic loads when cumulative plastic strain is relatively small, the inflection point of strain-cyclic number curve is proposed to determine the failure criteria of strain.