It is mainly achieved by controlling the quantity of the base currency. When the central bank uses monetary policies such as deposit reserve ratio, open market business and rediscount interest rate, it plays a role by affecting the reserve in the base currency. If the central bank raises the deposit reserve ratio, the reserves of commercial banks in the central bank will increase, while other conditions remain unchanged, the amount of base money they can use will decrease accordingly, thus reducing the money supply through the multiplier effect, causing deflation and inhibiting investment growth and economic development. If the central bank buys securities from commercial banks or the public in the open market, it will put the base money into the market. Although the reserve of commercial banks in the central bank will increase, the available base currency will increase even more, and the scale of credit will increase, thus increasing the money supply through the multiplier effect, promoting investment growth and economic development, and may lead to inflation.