A series of shaking table tests were carried out on a full‐size polymer ultrahigh voltage wall bushing. In addition, a corresponding finite element model of the wall bushing was established. Four different earthquake ground motions—the El Centro, modulated Landers, Taft, and an artificial earthquake acceleration time history—were adopted in the study. Test results indicate that the safety factor of the wall bushing is less than the stipulated value of 1.67 in the Chinese code under the peak ground acceleration (PGA) of 2 × 0.4 g, where the factor 2 is used to simulate the amplification effect of the valve hall on the seismic responses of the wall bushing. Necessary slackness should be allowed for the conductors connected to the wall bushing because of the large displacement of the bushing terminals. There are relative displacements between the central conductor and polymer insulators during an earthquake. Increasing the out‐of‐plane stiffness of sealing plates at the terminals of the wall bushing could decrease the relative displacements. Moreover, a theoretical vibration model of the wall bushing was developed to demonstrate that the rocking effects of the installation plate and flange bottom plate have an influence on the seismic responses of the wall bushing.