Abstract: This article analyses increment services affecting the optimal retail price and the market demand based on two retailers competing,then extends it to multi-retailer,and gets the parameters that make every retailer of the competing system to be optimal in profit,also gets the super limit of the price vector fluctuation.The conclusion is helpful for each side of supply chain to grasp the stability of the market.

Key words: supply chain, retailers competing, increment services, input-output function, pricing analysis