If you want a business visa, you need to bring an invitation letter/fax from a Chinese governmental department or government-authorized company.
For a multiple-entry visa, the invitation letter must be original. A single or double-entry visa is usually valid for entry within three months from the date of issue. Multi-entry visas are normally valid for six months and only issued according to official invitation letters for business visitors.
Types of business visa:
Single entry visa: valid for three months from issue.
Double entry visa: only valid for three months after issue, and the two visits have to made within three months.
Six month multiple entry visa: to get one you have to have been to China before and be able to provide a photocopy of your last visa from your passport. Multiple entry visas are valid for six months from when they are issued.
Extending your visa:
To extend your visa, head to the foreign affairs section of the local Public Security Bureau. The cost varies, but expect to pay around Yn250 (about £20).