Interest rates have a very important impact on the exchange rate, which is the most important factor affecting the exchange rate. We know that the exchange rate is the relative price between the two countries' currencies. Like other commodity pricing mechanisms, it is determined by the supply and demand relationship in the foreign exchange market. Foreign exchange is a kind of financial asset, which people hold because it can bring the benefits of capital. Under the conditions of open economy, the scale of international capital flows is huge, which greatly exceeds international trade volume, indicating the great development of financial globalization. The impact of interest-rate differentials on exchange rate movements is more important than in the past. When a country tightening credit, interest rates will rise, character formed in the international market interest rate difference, will cause the short-term funds internationally mobile, capital generally always is flowing from countries with low interest rates to countries with high interest rates. Because economists understand earnings as actual material wealth increase, accounting experts think the output value of more than the difference between the input value is profits, there is a contradiction and two kinds of income concept. The specific performance is: The investment quantity is the decreasing function of interest rate, saving is the increment function of interest rate, and the change of interest rate depends on the equilibrium point of investment quantity and saving amount. Keynes's theory of money supply and demand decided that interest rates were a monetary factor rather than an actual factor.