This paper investigates a one-supplier-one-retailer supply chain which has been coordinated with quantity discount contract. But when an emergent event causes demands disruption faced by retailer and makes the supplier's production cost fluctuate, if we do not take any responsive actions or just adjust the wholesale price, this coordination may be broken off. In this paper, we present an optimal strategy to response the ripple effect caused by the stochastic demands and production cost disruption simultaneously and propose an adjusted quantity discount contract to coordinate supply chain again.