Abstract: Substation arrester has a high vulnerability to earthquakes. An M_S (surface wave magnitude) 6.2 earthquake occurred in the Jishishan region (in Gansu Province of China)on December 18th, 2023. The massive arresters in a 750 kV substation lost electrical function by the earthquake. In order to study the seismic damage mechanism of the 750 kV arrester, this paper conducts a field investigation on the seismic damage of the substation and gives different damage modes and seismic vulnerability of the arrester. The finite element analysis is used to simulate the seismic response of the arrester under the action of earthquake, and the mechanism of seismic damage is analyzed. The results show that the failure modes of the arrester include the fracture of porcelain sleeve at the bottom of bush, the traction deformation of the conducting wire, and the short-circuit fault caused by the collision of adjacent equipment. With the increase in the stiffness of the steel support, the stress response at bottom of porcelain sleeve shows a trend of decreasing first and then maintaining the level. The relative displacement at the top of coupling structure with different fundamental frequencies (current transformer and arrester connected by conduct wire) reaches its maximum allowable displacement value, which leads to traction damage. The use of lattice steel support and seismic isolation devices can increase the seismic safety margin of arresters and improve the seismic performance of electrical equipment.