Abstract: To effectively reduce the damage of personnel and equipment in civil defense engineering subjected to blast shock wave, a shock isolation system with magnetorheological fluid dampers (MRFD) is established. MRFD can provide continuous and regulable coulomb friction, which is much efficient to reduce the accelerate response of the structure. The numerical simulation is completed by using a few semi-active control algorithms based on the instantaneous optimal active control algorithm. The results prove that the right semi-active control algorithms with suitable parameters can efficiently mitigate the structural response of acceleration.