Abstract: In order to improve supply chain efficiency,this paper analyses the supply chain,consisting of only one supplier andone retailer,with the control of virtual-third party.The virtual-thirdpartyplays the role of centralized control.We pay our attention to analyse,when the demand changes suddenly,how the supply chain reacts.At last we find that,the sudden change of demand does not impact the distribution,but the price will increase or decrease with the different degree of the change.

Key words: virtual-third party, two-stage supply chain, demand disruption, double moral hazard