Due to international economic exchanges such as trade, investment and tourism, there is always a relationship between monetary income and expenditure. However, different countries have different monetary systems. If you want to pay abroad, you must first buy foreign currency in your own currency. On the other hand, foreign currency payment vouchers received from abroad must also be converted into local currency to circulate in China. In this way, the exchange of domestic currency and foreign currency has occurred. The exchange rate of two currencies is called exchange rate or exchange rate. Central banks in western countries and China are institutions that implement foreign exchange policies, influence foreign exchange rates and often buy and sell foreign exchange. All commercial banks, banks specializing in foreign exchange business, foreign exchange brokers, importers and exporters, as well as their foreign exchange market suppliers and demanders, are engaged in various cash and forward foreign exchange transactions. All these foreign exchange transactions constitute a country's foreign exchange market.