The alliance of farmers and supermarkets is a business model of modern agriculture in which supermarkets are the carrier and platform. But the high transaction costs borne by farmers restrict the further development of the alliance of farmers and supermarkets. We point out that supermarkets helping farmers to reduce transaction costs should be the key to maintain a stable and cooperative relation between the two sides. In this paper, we take the impact of the wholesalers on spot market into consideration and construct the Bertrand game model based on spatial duopsony model to give the optimal strategy of supermarkets helping famers to reduce transaction costs.