With the development of electric power technology, information technology and military technology, the impact of cyber attack on electric power infrastructure has increasingly become a hot spot issue which calls both domestic and foreign attention. First, main reasons of the impact on power infrastructure caused by cyber attack are analyzed from the following two aspects: 1) The dependence of electric power infrastructure on information infrastructure makes cyber attack issues in information field likely to affect electric power field. 2) As regards to the potential threat sources, it will be considerably profitable to launch cyber attacks on electric power infrastructure. On this basis, this paper gives a classified elaboration on the characteristics and the possibilities of cyber attacks on electrical infrastructures. Finally, the recently published actual events of cyber attacks in respect of threat sources, vulnerabilities and assaulting modes are analyzed and summarized.