A method to calculate the earthquake damage index of substation according to the damage states of high voltage electrical equipment and buildings in substation was proposed in this paper. The seismic damage state of 121 substations of 110kV or above in Chengdu,Mianyang,Deyang,Guangyuan and Aba area in Wenchuan earthquake were analyzed. The seismic damage grade was evaluated according to earthquake damage index. The seismic vulnerability curve of substation based on peak ground acceleration was fitted by using lognormal distribution cumulative function. The calculated results show that when the seismic intensity is below Ⅶ,the damage state of substation and transmission lines is only in basically intact or slightly damage state,and no moderate damage or above damage grades occurs. While the seismic intensity increased to Ⅷ substation begins to suffer severe damage. When the intensity reaches Ⅸ,a small number of stats to show severe damage,and many substations are in moderate damage state. At intensity Ⅹ or above,most substations are severely damaged or even completely damaged.