As a foreign visitor to China you may require vaccinations and possibly anti-malarial medicine - certain parts of China are considered at risk. You should consult a specialist before you depart, but remember that some vaccinations take up to three months to become effective.
Some advice on how to stay healthy while traveling is available on these sites.
http://www.cdc.gov/travel/ - Travel health information from the Centers for Disease Control and Prevention. Includes reference material, recommendations by geographic region, and much more.
http://www.who.int/ith/ - The World Health Organisation's website on international travel and health issues.
http://www.high-altitude-medicine.com/ - The High Altitude Medicine Guide provides current medical information on the prevention, recognition, and treatment of altitude illness, as well as other health issues affecting travellers to high mountainous regions of the world.
http://www.tripprep.com/ - Also known as Travel Health Online, this site will help you have a safe, healthy adventure. Loads of useful information organized into three categories: Destination Information; Traveler Information; and Travel Medicine Providers (in the U.S. and around the world)