Abstract: In the displacement-based seismic design method for the pile-supported wharves, the key is to determine seismic displacement demand accurately and reasonably. In the displacement demand analysis methods, the nonlinear time-history analysis method can address the uncertainty of the ground motion well. However, due to the complex pile-soil interaction, the computation cost will be huge when the time-history analysis is carried out directly on the wharf structures. In order to estimate the seismic displacement demands of the pile-supported wharves with simplicity, an equivalent single-degree-of-freedom (SDOF) model for nonlinear time history analysis is proposed in this study. The simplified model is able to represent the deterioration of strength and stiffness for the wharf, as well as the dissipated energy of soil, whose restoring force is determined by the cyclically lateral loading analysis. To validate the applicability and accuracy of the proposed SDOF model, the nonlinear time history analyses of two typical wharves and counterpart SDOF models are carried out to compute the maximum displacements with an ensemble of 60 earthquake wave records, respectively. The validation process reveals that the displacements from the SDOF models correlate well with those of wharves, and the average values of their displacement ratios are close to unity with relatively low variability.