Banks certainly earn the difference, because foreign exchange trading is also a kind of banking business. For each kind of foreign exchange cash and cash, the bank has a buying price and a selling price, which depends on the foreign exchange quotation of the bank on that day. To put it simply, if you change RMB into foreign exchange from the bank, you buy it from the bank. Of course, it will be settled according to the selling price of the bank. If you want to change the inexhaustible foreign exchange into RMB, you can sell it to the bank. Of course, it will be settled according to the bank's purchase price. When you buy and sell, you will naturally lose the difference.