This study proposes a simplified analytical model to analyze the nonlinear dynamic behavior of soil-pile-superstructure interaction systems under seismic loading. The model specifically captures the plastic hinge formation at the pile head and bottom and the associated stiffness reduction under a single seismic loading. This stiffness reduction helps to limit the maximum inertial forces acting on the superstructure and effectively control the structural response. The model is calibrated for saturated sandy soils with a relative density of 40%, providing a basis for future studies on the behaviors of piles in denser soil environments. To validate the proposed analytical model, reduced-scale RC pile models were tested under seismic loading in a 50G centrifugal field. The experimental results showed the plastic hinge formation at critical points with a corresponding gradual stiffness degradation, which is in close agreement with the analytical results. This agreement supports the model’s practicality for evaluating the non-linear response of RC piles in liquefied soils. These results provide valuable insights for optimizing pile foundation design and implementing secondary seismic measures, especially in regions that are prone to soil liquefaction.