Abstract: Through the continuous extension of the loss caused by the disruptions and the extension of the partial information of end time, the paper explores when managers should activate contingency plans based on the multi-attribute decision making method and concentration of loss function. In the absence of information of loss function about unexpected events, the author tries toconstruct anactivating model by taking the theory and methods of online decision making. The author also uses the competitive ratio to prove the effectiveness of the model. On this base,further numerical analysis shows the effectiveness of contingency plans.