A foreign exchange bill refers to a foreign exchange currency pair containing US dollars. These seven kinds of direct foreign exchange are euro, pound, dollar, yen, dollar, Swiss franc, Australian dollar, New Zealand dollar, US dollar and Canadian dollar. Direct foreign exchange currencies account for more than 80% of the total trading volume in the foreign exchange market, among which seven direct foreign exchange currencies account for more than 85% of the trading volume. The main reason is that these seven direct foreign exchange currencies are the most suitable direct foreign exchange varieties that investors are familiar with.