This paper investigates new challenges that a blackout defense system has to confront under extreme external conditions and the way to cope with them. As the first part of the two-part paper， it reviews the defense system in operation， summarizes the characteristics of blackouts under extreme external circumstance， and points out the difficulties that the defense system designed for general faults has encountered. An idea is presented to extend the defense system's activating time scale from both sides， namely the power system planning stage for long term preventive countermeasures， as well as the restoration control stage in case of the power system disintegrated. It is also proposed to further upgrade functions of the defense system on aspects of wide-area information， simulation analysis and decision-making support.