Beijing International Jewellery Fair 2013

Dear sir/madam
Im srilankan citizen and my business is exporting gems. Im willing to visit Beijing International Jewellery Fair 2013. I have been visited to india/thailand/malaysia/United Kingdom/madagascar and singapore on buying, selling gems and participated in gems shows such as Beijing International Jewellery Fair.

My questions are:-
*what kind of visa should i request (busines/visit) ?
*what are the documents to submite?
*do i need any invitation letter?( visiter register confirmation letter for show is enough or need any other invitation)
* what are required addditional documents?

Please guide me