Holding US Treasury bonds faces higher opportunity cost or actual cost. The average annual yield of US 10 national debt is 3%-6%, which is far lower than the average yield that investors can get by investing in stock index or direct investment. For China banks, holding US Treasury bonds has a more realistic cost. This is because the accumulation of foreign exchange reserves of the central bank will lead to an increase in foreign exchange holdings. In order to prevent the impact of the increase in foreign exchange holdings on the domestic base currency, the central bank usually uses the method of issuing central bank bills for verification, which has interest costs.

As for the China government's purchase of US Treasury bonds, it does not pay attention to the interest rate of investment, but hopes to stabilize the exchange rate of its currency against the US dollar to protect the country's export industry. There are two main ways to prevent RMB from appreciating. One is to sell RMB in the market or buy dollars in large quantities. This method can't last for a long time, and the other is to buy a lot of American debt every year to prevent the RMB exchange rate from rising.