Many U.S citizens buy the Chinese products that are produced which keeps China in business. Without the purchasing of their items from the 300 million people out of the U.S, China will have a lower economy.
The U.S depends heavily on China to support them with loans of money to operate the country successfully, while still helping China keep a stable economy. If not the mutualistic interactions between the two countries will fade away.
Since the U.S. is one of the most powerful countries in the world, China wants to be their ally to stay in a safe position in the economy rankings. With these two countries partnering up then wish to maintain a peaceful world.
The reason why China produces a lot of items within their country is because of the term "workshop of the world". This quote shows how effectively China's cooperation with labor is. China now produces what they produced in one year in 1988 in a day!
When U.S. people buy the products that the Chinese people produced they save a lot of money. Statistics show that American have saved 600 billion dollars from buying chinese products.
If you can't paint the picture as of now, China and the U.S need each other to operate their countries properly and effectively. When one country doesn't do their part the other country is affected.