Abstract: Based on the particular characteristics of the Electrorheological Fluids (ERF) tunable damping, the structure of ER isolator and its working principle are discussed. The two estimative parameters of isolation system-dynamic stiffness and loss angle are determined applying bond graph theory to dynamic simulation and modeling. It is proved that ER isolator will work well in both in the low and high frequency zones. The "smart" ER fluid can tune its viscosity instantly with controllable electric field and thereby gain ends in active isolation and enlarge the isolation frequency domain efficiently by measuring the system damping.