This paper researches the optimal start-up time of emergency plan adopting online method. In view of this problem, it establishes respectively mathematical models of the single enterprise and the simple supply chain enterprises. And then competitive ratio is introduced to illustrate the effectiveness of start-up strategies. When the whole supply chain enterprises are considered as the research objective, the time asynchronous phenomena when launching the preplan appear between the single enterprise and the whole supply chain. Aimed at this phenomenon, it puts forward coordination mechanism, realizes the optimal response of the whole supply chain for emergencies, and controls the loss emergencies causes to the minimum. The research result has theoretical guidance and practical application value.