Abstract: Because the soft clay soil usually has a significant rheological effect, the deformation of the soft clay is divided into two parts, i.e., that caused by the effective stress change and that caused by the secondary consolidation. A new stress-strain relationship is thus derived. Based on the Davis's consolidation theory, a one-dimensional nonlinear consolidation equation with consideration of the secondary consolidation is established. The newly proposed equation is solved analytically and its reliability is verified by comparing with the numerical results. The influence of the secondary-consolidation on the settlement of the soft ground is studied. The results show that both the dissipation rate and the consolidation rate obtained by the present method are reduced as compared with those obtained by the traditional method, and the neglect of the secondary consolidation will underestimate the post-construction settlement of the soft clay foundation.