The　operation　of　power　system　will　inevitably　be　influenced　by　a　variety　of　natural　disasters　(e.g.,　typhoon,　forest　fire).　Those　disasters　will　dramatically　change　the　operating　environment　of　power　system　and　increase　probability　of　the　occurrence　of　specifically　faults.　It　is　important　to　make　use　of　disaster　forecast　inform　to　make　safe　analyses　and　risk　evaluation　and　establish　early　warning　mechanism,　emergency　response　mechanism,　rapid　post-disaster　restoration　and　reconstruction　mechanism　of　natural　disaster.　The　probability　of　unit　fault　will　seriously　increase　in　the　process　of　natural　disaster.　As　the　security　is　measured　by　estimating　the　influence　on　the　power　system　caused　by　contingency,　contingency　set　in　safe-evaluating　will　have　a　direct　influence　on　state　evaluation　results　and　control　strategy　option.　The　contingency　constructing,　filtering,　ranking　method　according　to　particular　natural　disaster　forecasting　information　is　discussed　in　this　paper.　It　will　help　to　achieve　on-line　security　forewarning　in　power　system　and　make　it　useful　to　make　the　pre-decision　of　dispatching　according　to　the　development　of　specific　disasters.　©　2008　DRPT.