Abstract: Based on the constitutive equation of magnetictive material,the model of the whole Active Vibration Isolation System (AVIS) was put forward and its dynamics and stability of the control system was analyzed.Simulation results show that the parameters of the upper mass have much more influence on the active force of the actuator,and stiffness of the lower mass effects isolation performance while the absolute acceleration of the middle mass is adopted as feedback.For the feedforward control scheme,system stability would not be influenced by the frequency variation,though the feedback link can reduce its stability margin.In the feedback control scheme,the time delay effect of the secondary path may cause the system unstable when the vibration frequency increases.