Abstract: The pile-shaft is a substructure widely used in bridge engineering. Under earthquake, the pile may yield if the capacity protection design principle is not well followed. Due to the complex soil-pile interaction in modeling and analysis, it is still difficult to predict the seismic demand of piles based on the yielding moments of piers. Therefore a coupled soil-pile-structure model are adopted to investigate the ductility seismic design method of pile-shafts with a focus on the simplified seismic demand prediction method. Investigations are conducted on the bending moment distribution under different earthquake intensities to determine pile-shaft demand parameters, and extensive parametric analyses are performed to understand the mathematical relationship between pile-shaft demand parameters and soil/structural sensitive parameters. A simplified seismic demand prediction method is proposed.