Usually, a freely convertible key currency, which is most commonly used in international economic transactions and accounts for the largest proportion of foreign exchange reserves, is chosen as the main target, and the exchange rate is determined by comparing it with the domestic currency. This exchange rate is the base exchange rate. Key currency generally refers to a world currency, which is widely used in pricing, settlement, reserve currency, freely convertible and internationally accepted currency. At present, the key currency is usually the US dollar, with the exchange rate of the domestic currency against the US dollar as the benchmark exchange rate.

The benchmark exchange rate is the exchange rate between the local currency and the most commonly used basic foreign currency in foreign economic exchanges. At present, countries generally use the US dollar as the basic foreign currency to determine the benchmark exchange rate. Before August 2006, China's benchmark exchange rates included RMB against the US dollar, RMB against the Japanese yen, RMB against the euro and RMB against the Hong Kong dollar. After August 2006, the benchmark exchange rate increased the exchange rate of RMB against the British pound.

The benchmark exchange rate of RMB is the benchmark exchange rate of major trading currencies (US dollars, Japanese yen and Hong Kong dollars) against RMB announced by the People's Bank of China according to the weighted average price of US dollars against RMB formed in the inter-bank foreign exchange market the previous day, that is, the market transaction middle price.