Because of the special position of electric power industry in national economy and social life, electric power information security has been given particular attention. In recent years, the security defense of Electric Power Information System has been all under the principle of security area classification, which applies different security defense measures for the information systems in different security level. However, because of lacking theory guidance, the recent method of security area classification is not in accord with the requirements of real production and management, and security threaten occurs at times. In order to meet the requirements of real production and management and the needs of security area classification defense in Electric Power Information System, based on the theory of network business security, a new security area classification model of Electric Power Information System has been proposed, and the access rules of the information transmission and sharing between different security areas have also been proposed. The new security area classification model can provide theoretical basis for security area classification in Electric Power Information System, and can deal with the conflict between the requirements of real production and the needs of information security.