With the improvement of the intellectualization and overall scale of power grid, modern power system is more and more vulnerable to the threat of high-altitude electromagnetic pulse. Once the key link fails, cascading reactions may occur, resulting in large-scale blackouts. For different electric equipments, their effect modes and threat levels are also different, thus it is necessary to carry out classification research. According to the different effect modes of electric equipments under electromagnetic pulse, this paper divides the equipments into Supervisor Control And Data Acquisition (SCADA) system and relay protection equipment, coil type equipment including transformer and so on, lightning arrestor including line type and equipment type, and other types of equipment. Their effect mechanisms are analyzed in detail. Secondly, considering that there are many kinds of effect levels under the threat of high-altitude electromagnetic pulse, different effect classification methods and multi-level effect evaluation model are introduced. Finally, considering comprehensive impact of vulnerability and importance and the cascading effects among equipment, the fail are links of power system under E1 and E3 are summarized and analyzed, respectively.