International trade theory is a very important theory in economics that provides a solid theoretical foundation for the development of international trade. Through the establishment of an index distribution probability model for international trade balance, Cauchy distribution probability model and Rayleigh distribution probability model, a country's foreign trade balance is considered a "small probability event" in this paper, and "a country in deficit or in surplus is a normal form". On this basis, empirical tests are carried out. The results show that the economic benefits of international trade fluctuate around the balance, which supports the content of probability models.