Unexpected vibration that occurs in the civil structures may damage the structure and even endanger the people's life. To address this problem, a semi-active vibration control method based on tunable electromagnetic damper is proposed in this paper. Therein, a tunable electromagnetic damper is established that integrates a permanent magnet synchronous motor (PMSM) and a ball screw, which are connected by a coupling. When the system is affected by vibrational excitation, the ball screw will drive the rotor of the permanent magnet synchronous motor to rotate. To suppress the vibrational excitation, the duty ratio of three-phase voltage source converter on the load side of PMSM is controlled by the vector control and SVPWM algorithm, and the electromagnetic torque with tunable properties of 'damping, inerter, and stiffness' can be generated by PMSM. In addition, an experiment platform of tunable electromagnetic damper is built, wherein the PMSM is controlled using digital signal processor TMS320F28335. Extensive simulation and experimental studies verify the tunable function of damping coefficient of tunable electromagnetic damper and the effectiveness of control method.