The residual displacement magnitude is a vital indicator reflecting the self-centering ability of the seismic isolation layer and a key criterion for evaluating the post-earthquake normal functionality of main structural buildings.Earthquake damage surveys have shown that isolation bearings commonly experience residual displacement after seismic activities,leading to incomplete self-centering of the isolation layer.To elucidate the mechanism of residual displacement generation in the isolation layer,a free vibration decay dynamic model was established based on the Coulomb friction single-degree-of-freedom (SDOF) system and the bilinear hysteresis characteristics of the isolation layer.A simplified formula for calculating the maximum residual displacement was proposed and validated through rigorous numerical simulations, providing theoretical support for rationally assessing the self-centering capacity of the isolation layer. Results indicate that the distribution of residual displacement in the isolation layer is highly scattered, yet its maximum value can be ascertained.The influencing factors involve the nominal yield strength Qd, initial stiffness k0, post-yield stiffness k, and damping ratio ξ. The proposed simplified formula offers practical guidance for engineering design.