This is the time value compensation of money. The difference between foreign exchange buying and selling is the bank's expenses and corresponding profits. First, the forward transaction occurs in the future (the delivery date is in the future), that is, to obtain the price difference in the future, there is price compensation to convert the future profit value into the present value; Second, the credit risk of spot trading is very small, and the risk of forward trading is relatively large. As a part of risk compensation, the value is also reflected in the price difference; Third, after the forward transaction, the bank carries out risk management on the positions generated by the forward, and the management fee is greater than the risk management fee of the spot transaction.