The paper analyses the impact on the efficiency of tariff policy under the differentiated duopoly model of Dixit,and considers the rationality that the export firm chooses the strategy of the product diffferentiation under the Cournot and Bertrand competition.The propositions show that the product differentiation can lower the rent transfer efficiency by the tariff policy under the Cournot competition but can heighten the optimum tariff under the Bertrand competition.However,the increase of the ...