Abstract: A series of quantitative indices denoting the direction characteristic of active force of AMD (Active Mass Driver) control system were developed first, which include direction relation between active control force and relative velocity or displacement of AMD mass, peak and RMS (root mean square) values of active force with respect to inertia force of AMD subsystem and so on. Under the background of one SDOF structure controlled by an AMD system using LQR (Linear Quadratic Regulator) control algorithm, three representative work cases were then designed to study the interaction relationship among characteristic indices of active control force of AMD system, structural control effect, weighting parameters of control algorithm and system input loads, etc., thereafter, numerical results were systematically analyzed and summarized. Finally, based on quantitative results and qualitative analysis, it is found that it is not feasible to replace active actuators in AMD systems by semi-active variable damping devices to achieve equivalent active control performance.