GDP=C+I+G+(Ex-Im), foreign trade multiplier =1(1-marginal propensity to consume+marginal propensity to import). No matter which formula you look at, the increase of exports will lead to the balanced growth of GDP. Generally speaking, the increase of net exports can stimulate the economy, and the surplus generated can be used for investment and consumption ... and so on. In short, as long as net exports increase, the trade balance will improve.

In the sense of economics, open economy refers to the form of economic exchanges between a country and foreign countries, and there is a close relationship between domestic economy and foreign economy. There are three levels of open economy: (1) the product market is open, that is, the import and export of product trade; (2) The capital market is open, that is, capital is allowed to flow freely; (3) The factor market is open, especially the labor factor can flow freely. Few countries, especially developed countries, open factor markets, and the prohibition of factor markets is to protect the employment of their nationals. Under the condition of open economy, the position of external equilibrium in monetary policy has been significantly improved. First of all, the development of China's opening to the outside world and the improvement of its economic openness have significantly increased the influence of foreign economic sectors on macro-balance, thus forcing the central bank to pay more and more attention to external balance while paying attention to internal balance. Monetary policy needs to take into account the two goals of internal and external balance, which requires the central bank to pay attention to using different control means when applying various policies. Obviously, it is obviously more difficult to implement monetary policy under the condition of open economy.

Secondly, under the condition of open economy, maintaining the stability of currency actually includes the internal stability and external stability of currency. The external stability of currency value is subject to the change of balance of payments, which affects foreign exchange reserves, and then restricts the delivery of base currency, thus affecting money supply. Third, with the improvement of economic openness, the transnational transfer of international capital is accelerated, especially the frequent flow of international speculative capital (open or hidden), which not only causes the expansion and virtualization of financial transactions, but also intensifies the chaos of financial order and the instability of economic system. Joining WTO will promote the opening of China's capital account and allow foreign banks to do business in China. Monetary policy will also face new challenges brought by international capital flows. Therefore, under the condition of open economy, the goal of monetary policy will be more focused on achieving external economic balance and international balance of payments.