You should go to the Chinese embassy in Colombo. The documents you need are: one passport valid for at least half a year, a passport photo and an application form for China, an invitation letter/fax from your contact in China is required for business purpose. For applying a multiple entry visa, an invitation letter from a Chinese governmental department or a competent company is required.

Thank you very much Mr.Kyle for your prompt response. I have all the documents except invitation letter from Chinese governmental department. I will apply for single entry. Do I need to get that invitation letter.

for single entry visa, you just need an invitation letter from a unit or company that you are going to visit in China. That is enough.