What is the procedure to apply visa for attending the CIHF2011 fair in ZHENGZHOU as a buyer.

You have to have a business partner in China who can obtain the "Invitation Letter of Duly Authorized Unit" or "Confirmation Letter of Invitation", it is the most important document for China Business Visa Application.

Otherwise, it is almost impossible for you to get a business visa to China. The visa rule for Sri Lanka nationals is very strict.