Type -L type visa requirements

Generally, the documents you should provide include:
1. a passport with at least two blank pages and valid at least six months.
2. an application form affixed with a passport size recent photo.
3. an invitation letter from an authorized Chinese organization, company or Chinese citizen. If you can't provide invitation letter, round-trip air tickets and hotel reservation are needed.

PS: some nationals are required to provide travel insurance (100 USD per day).

If you plan to join the trade fair, I am afraid that you need to apply for a F type.