The buyer-supplier relationship plays a great role in most economic systems.The buying firm usually tries to find a new supplier who provides products with satisfying quality and lower price.A broad branch of literature deals with the development of buyer-supplier relationships,but limited research is on the circumstances under which a buyer should terminate such a relationship and switch to a new supplier.In this paper,the incentive compatibility constraint (IC)which induces the entrant supplier to report his true cost is considered,and the participation constraint(PC)which ensures the entrant supplier to get at least reservation profit is taken into account.Then the supplier switching model is set up to minimize the buying firms total procurement cost which includes the transfer payment to the incumbent supplier,the payment to the entrant supplier and the switching cost,and the buying firms switching cost is considered as a function of the switching quantity.With the theoretical analysis of IC,PC and the proposed model,the optimal supplier switching strategy can be obtained.Finally,a numerical example is given to illustrate the effectiveness of the proposed model and the switching strategy.