In a country's foreign economic activities, the foreign exchange income earned constitutes a country's foreign exchange supply, and conversely, the foreign exchange expenditure delivered constitutes foreign exchange demand.

Theoretically speaking, foreign exchange supply and demand refers to the amount of foreign exchange provided or demanded by local currency and foreign currency at a certain exchange rate. The relationship between foreign exchange supply and demand directly affects the trend of foreign exchange prices and plays a decisive role in a country's international balance of payments. Therefore, foreign exchange receipts and payments have generally become one of the goals of macroeconomic policies in various countries.

Generally speaking, foreign exchange supply mainly comes from the following activities: 1. Commodity export is the main source of foreign exchange supply; 2. Labor export, such as contracted projects, transportation, banking, insurance, dividends, interest and other income; 3. Capital export, including direct investment and indirect investment input; 4. Foreigners come to their own countries to visit and study; 5. National remittance; 6. Expenditure of foreign government personnel in China; 7. Gifts, economic and technical assistance, charitable donations and military reparations from foreign governments.