A mathematic model of maximizing additional value is set up in this paper.By comparing it with the economic effects of profit maximization,the author makes analyses of those of additional value maximization from the view of both domestic trade and international trade.It's concluded that additional value maximization has both industry structure and welfare effects,and that it is in harmony with profit maximization in domestic trade but is not necessary in international trade.The author argues that profit maximization is not effective in international trade and some suggestions about policy-making are put forward.