Abstract：As far as a big country is concerned, the relationship between regional trade and international trade can be concluded as:On one hand, regional trade and international trade can replace each other to some extent; and the two can promote each other on the other hand, and the development of regional trade can enhance nation Competitiveness.
This article can be divided into three parts. The first part explores the replaceable relationship of the two kinds of trade. We suppose there are two regions in a big country; the endowments of the two countries and the regions are different. According to the comparative advantage theory, regional trade or international trade is inevitable, but the trade pattern is uncertain.
The second part analyzes the promotional relationship of them.The article argue that international trade can promote the development of domestic regional trade on one side; on the other side, through regional trade, companies can enlarge production and realize economies of scale and external economies, domestic companies thus can lower the production cost and can enhance the competitiveness of the products. Thirdly, with the development of regional trade, the division of labor and specialization between the two regions make the rewards of companies increase progressively. Rewards increase progressively means higher productivity and lower production cost.All these factors can enhance the competitiveness of the products in international trade and thus heighten the nation competitiveness in the world.
The third part takes the Unite States as an example to illustrate the important role that the domestic regional trade plays in nation competitiveness. Before independence, the amount of regional trade among the colonies was very small, after independence, regional trade took the place of international trade partly and grew very fast.
