Abstract: When the theories of contract economics are applied to analyze the problems of international trade, more attention is paid to the macroscopic effects of contract behaviors. Thus the research of the effects of reasonable behaviors on the microscopic level of international trade may have some innovation. When international trade occurs between the two parties of import and export within the common monetary area, there is no obvious difference between the contract behaviors and the internal trade behaviors, for the single currency is used and the freight is rather cheaper. If considering the transportation costs and other costs as well as exchange rate and other factors, the best quality level of the contract will be changed, which is resulted from the distribution of the surplus to a third party and changes of evaluation on the type of the importer by the exporter due to exchange rate fluctuation. Generally, transportation and other costs will worsen the contract condition while the effects of exchange fluctuation are uncertain.

Key words: contract theory; single currency; freight; exchange rate