<p>This study introduces an innovative design of a Variable Damping-Inertial Eddy Current Damper (VD-IECD) to address the specific needs of base-isolated structures under long-period earthquake excitations. The VD-IECD combines nonlinear eddy current damping with inertial effects, offering a unique approach to energy dissipation and vibration control, expanding the application scenarios of existing damping technologies. In the context of current research, effectively responding to long-period earthquake excitations remains a critical challenge, and existing dampers have demonstrated certain control effectiveness. This study proposes a new damping design concept to further optimize the seismic performance of the system. To enhance control efficiency, a semi-active control strategy is employed, enabling the VD-IECD to perform well in reducing structural vibration responses, especially in complex seismic environments, thereby improving the stability and safety of the isolation system. Through a frequency domain random vibration response analysis of a single-degree-of-freedom (SDOF) structure, as well as numerical simulations under long-period earthquake conditions, the results indicate that the VD-IECD not only significantly reduces the displacement of the isolation layer but also effectively decreases the seismic response of the superstructure. This demonstrates the device’s potential in enhancing the overall safety and reliability of the structure, providing a powerful alternative for seismic design in base-isolated structures.</p>