The company in China should send you an invitation letter with the stamp of the company, the copy of his business license, the company in China also should go to the Foreign Affairs Office or Committe of Foreign Trade and Economic Relations to apply for an official invitation letter for you. If you have the above documents, you just need prepare
A. One completed visa application form;
B. One recent passport sized photo;
C. A valid original passport with blank pages.
then go to the Chinese embassy in Colombo to apply for business visa f visa.