International trade theory is an important part of international economics, which is microeconomics under open conditions. International trade theory focuses on the exchange of goods and services between countries, the causes and consequences of international commodity exchange, and related policies. The research scope of international trade theory also includes the international flow of production factors and the international transmission of technical knowledge. Factors of production and technical knowledge have their own international markets as a particular commodity on the one hand, and play an important role in the production of goods and services as factor inputs on the other. International trade theory also studies the interaction of economic growth, technological change and trade, and analyzes the causes and results of changes in international trade in dynamic terms.

  Factors affecting international trade：

1. Factors affecting a country's export trade

(1) The abundance of natural resources

(2) The level of production capacity and technology

(3) the level of exchange rate

(4) the state of the national economy, the level of international market demand and changes in the structure of demand

2. Factors affecting the import trade of a country

(1) A country's economic aggregate or total output level

(2) The level of the exchange rate

(3) The level of the country's import trade with the supply of goods in the international market and the level of prices

  International trade theory is the theory that reveals the causes, structure and benefits of international trade. The development of international trade theory has roughly gone through four major stages: classical, neoclassical, neo-trade theory and emerging classical international trade theory.
  Classical and neoclassical international trade theories are premised on assumptions such as perfectly competitive markets, emphasize the mutual benefits of trade, and mainly explain inter-industry trade. After World War II, with the new dynamics of global trade as an opportunity, new trade theories emerged, explaining new trade phenomena from the perspectives of imperfect competition, economies of scale, and technological progress. Emerging classical international trade theory, on the other hand, explains trade in terms of specialized division of labor, and seeks to unify traditional trade theory and new trade theory within the framework of emerging classical trade theory.

  Classical international trade theory arose in the mid-18th century and was developed based on the critique of mercantilism, mainly including Adam Smith's theory of absolute advantage and David Ricardo's theory of comparative advantage. Classical trade theory explains the causes, structure and distribution of benefits arising from international trade from the perspective of labor productivity.

  During the period of primitive capitalist accumulation in the late 15th and early 16th centuries, the mercantilist (Mercantilism) view of international trade emerged, also known as the trade differential theory (late mercantilism), which centered on the pursuit of trade surpluses, represented by Thomas Mun of England. Mercantilism believes that the only form of wealth is gold and silver, the amount of gold and silver is the only measure of a country's wealth, and the main channel to obtain gold and silver is international trade. The main way to obtain gold and silver is through international trade.