In order to study the effect of foundation liquefaction on the vibration characteristics of a small height-width ratio isolation structure system， the seismic response process of a small height-width ratio isolation structure system of pile foundation on liquefac tion site is reconstructed by shaking table model test. The seismic response of the isolated structure during the process of soil lique faction is analyzed. The results show that： the first natural frequency of the isolated structure on the liquefiable soil foundation is significantly higher than that on the rigid foundation， and the damping ratio is also significantly higher than that on the rigid founda tion. The isolation layer on the liquefiable soil foundation plays a significant role in amplifying the horizontal acceleration response of the pile foundation， and the isolation effect disappears. However， the isolation layer plays another significant role in reducing the rotational angular acceleration response of the pile foundation. The distribution law of the peak acceleration amplification factor of the floor of small height-width ratio isolation structures on the liquefiable soil foundation is obviously different from that on the non liquefaction foundation， which shows the characteristics of bending amplification， and the amplification coefficient of peak accelera tion on the top floor of the isolation structure increases obviously. The maximum inter?storey displacement response of isolated structures on the liquefiable soil foundation is far greater than that on the rigid foundation under strong earthquake action， which may lead to the isolation structures based on the assumption of the rigid foundation not meeting the requirements of seismic design when the soil foundation liquefies.