In recent years，extreme natural disasters occur frequently，thus it is necessary to extend the defense scheme for defending the natural disasters.This paper concludes the impacts of natural disasters on power system operating reliability，analyses the failure mechanism of power system equipment，builds the mathematical models of correlation taches，and extracts the extended environmental information for blackout defense system.The scope of information acquisition of blackout defense system is expanded to macroscale and microscale meteorological information as well as geological information.The spatial-temporal distribution of electrical equipment failure probability is estimated on line based on the external background information，real-time operating conditions and environmental information.The spatial-temporal probability model modified on line takes the place of the yearly average probability model which is offline and fixed.The anticipated fault table of stability and adequacy analysis is adjusted on line so that the potential failures with high risks can attract more attention.Based on the catastrophe evolution mechanism，the risk of power system reliability is dynamically assessed，and the early-warning of a power system is realized，hence the decision support function can adapt the natural disasters.