All visitors traveling to mainland China whether for business or pleasure, require a visa. Your passport must be valid for at least 6 months after the duration of your intended stay. Visas are issued through Chinese embassies and consulates overseas. It's very difficult to obtain a China visa at the Chinese border entry points.
Single-entry China visas are usually valid for 3 months after the issue date, and will permit you to stay in China for a maximum of 30 days. This visa will allow you to travel as a tourist or conduct general business activities. Most people need only to apply for a single-entry.
You need to apply for 'double' or 'multiple entry Visa if you need to leave and re-enter mainland China. Please keep in mind that when you leave for Hong Kong, Macao from mainland China, you will need to have 'double' or 'multiple' entry Visa.
No Visa is required prior to entering Kong Hong, a Visa will be issued upon arrival. Travelers leaving for Hong Kong, Macao from mainland China need a new Chinese visa or a multi-entry visa to re-enter the mainland.
Visas are not required for transit passengers who hold tickets and have booked seats on international airliners flying on route to a third country no more than 24 hours in advance.
You should check with the Chinese embassy in your country of residence for the most up-to-date information: China Visa Application