When the amount of foreign currency bought by domestic investors in local currency is much larger than the amount of foreign currency sold by investors, the local currency will depreciate against foreign currency. In order to slow down the depreciation of local currency, the central bank can put foreign currency in foreign exchange reserves into the market, that is, sell foreign currency to the market, thus improving the supply and demand relationship between local currency and foreign currency in the market and alleviating the decline of local currency against foreign currency.