You can exchange foreign currencies for RMB cash in advance in the country or region where you are before bringing it into China (each visitor is allowed to take up to 20,000 yuan ($2789.43) in cash in or out of China).
Also inside China you can exchange foreign currencies for RMB cash at commercial bank branches, money changers, and self-service currency exchange machines at international airports, land ports, sea ports, and other entry ports, or withdraw RMB cash using international bank cards at ATMs in China.