The key of seismic fragility analysis for structure is to ascertain the structure response values under various earthquake ground motion levels.Due to the uncertainty of ground motions,a large number of ground motion records need to be statistically analyzed.The computation cost will be huge,especially when the seismic analyses are directly performed on wharf structures.In order to reduce the complexity of fragility analysis of steel pipe pile wharf,we proposed a single-degree-of-freedom (SDOF) model for seismic fragility analysis of steel pipe pile-supported wharves,which utilizes curvilinear backbone curve and Masing rule to mimic the restoring force characteristics.In order to verify the rationality and effectiveness of the proposed model,a steel pipe pile wharf structure is equivalent to the single degree of freedom model,and the fragility analysis of the prototype structure and the single degree of freedom model is carried out based on the cloud diagram method.The results show that the fragility curves of the two models are in good agreement.