The changes of the total amount and structure of the central bank's balance sheet can reflect all kinds of monetary policy operations. It is one of the important tools to study liquidity. By the end of April this year, about 58% of the central bank's balance sheet was foreign assets, mainly foreign exchange. The main reason we mentioned in the change of the main channel of base money delivery is that before 2014, the Central Bank of China continued to buy foreign exchange to deliver base money, resulting in foreign exchange becoming the main part of the central bank's assets, accounting for about 83% at the highest. After 2015, with the slowdown of capital inflow, the central bank's monetary policy tools dominated the change of base currency. In this process, the central bank increased its creditor's rights to commercial banks. At present, the creditor's rights of the central bank to other deposit companies account for about 31% of the total assets. Accordingly, the central bank's liability side is dominated by reserve currency, accounting for 84% of the total liabilities; Government deposits are another major part of the central bank's liabilities, accounting for about 11%. Between 2002 and 2010, the issuance scale of central bank bills expanded rapidly, and the return of money became the goal of the operation of central bank bill policy tools. At its highest scale, it once accounted for nearly 28% of the total debt of the central bank. After 2010, the central bank has used less and less central ticket tools, and some central tickets will not be renewed after expiration. At present, the scale of bills has shrunk to 95 billion yuan.