When the value of China's currency, the RMB, goes up compared to the U.S. dollar, China's exports to the U.S. decrease, leading to less money coming in. This causes China to spend more on imports, which increases the amount of dollars leaving the country. Over time, China ends up with fewer U.S. dollars, so they need more dollars, causing the U.S. dollar to become more valuable. This means the exchange rate of the RMB against the U.S. dollar goes down.