Considering a two echelon supply chain model under demand uncertainty and assuming the products are sold over a single selling season, we analyze the competition structure in a supply chain with one supplier and multiple retailers. We found out that when the supplier gives one retailer an extra chance to order products before the selling season, the competition form of the supply chain would change and the suppler can gain more profit. The equilibrium solutions of the models are gained through backward induction and the results are compared.