Cash leakage is a phenomenon that customers withdraw deposits from banks and ask for cash, so that cash flows out of the commercial banking system as a reserve. After obtaining the income, customers will always withdraw some funds from the bank and hold them in the form of cash, so that these funds will flow out of the banking system, which is called cash loss. When there is cash leakage, the deposit reserve of the banking system will be reduced, that is, the funds for banks to expand loans by absorbing deposits will be reduced accordingly, thus weakening the ability of banks to create derivative deposits. Cash leakage is mainly determined by the disposable income level of non-banking industry, the acquisition of expected opportunity cost, the degree of inflation and the service level of banking industry. The ratio of cash leakage to total demand deposits is called cash leakage rate. A high ratio means that more cash flows out of the bank, the cash reserves in the banking system are correspondingly reduced, and the derivative deposits created are correspondingly reduced. The low ratio means that there is less cash flowing out of the bank and more cash reserves in the banking system, thus creating relatively more derivative deposits. The influence of cash leakage rate on the creation of deposit currency of commercial banks is the same as the statutory reserve ratio, which is an important factor restricting the credit creation ability of commercial banks.