Seismic performance is meaningful for high voltage disconnect switch， which is vulnerable to the earthquake for its long span， great height， and flexibility. In this paper， a full-scale shake table test on 800 kV three-post disconnect switch is carried out to obtain its dynamical properties and seismic responses laws. The effect on disconnect switch’s posts caused by the main blade is studied in different direction via characteristics of acceleration amplification factor and the spectrum analysis method. The results indicate the space lattice tilted structure form can limit the adverse impacts on seismic responses induced by the height and flexibility of the equipment. Meanwhile， after the main blade closed， a certain constraint effect will occur in the along-span direction， while in the across-span direction constraint effect is weak. The constraint effect can amplify and reduce the seismic responses of the post with blade and the post with fixed contact respectively.