There are numerous ways to move money internationally, but China puts restrictions on how much currency can be moved out of the country in a given year.
The most direct way is to process an IBAN/SWIFT/Wire transfer from a Chinese bank to a U.S. account. This requires that your friend has a USD-denominated bank account to receive the money, and the bank charges a commission, but that commission usually has a cap. China Construction, ICBC, Bank of China, etc. all support this method.
Less direct is to convert the money into a digital currency that can be moved more easily. One common method is to operate a U.S. and an international PayPal account simultaneously. Yet again, you'll need a U.S.-based bank account tied to a U.S. PayPal account, and a Chinese PayPal account tied to a UnionPay-compatible bank account. Send the money from your bank to your international PayPal, then from your international PayPal to your U.S. PayPal account.
Less direct, still, but perfectly doable is to purchase bitcoins with RMB, then sell them for USD from the U.S. That has no commission aside from transactional costs involved in conversion.