how do i get my document authentication by chinese embassy?

Yes, it's a totally different process from visa application. Just follow the steps below:
1) Documents should be notarized by any notary public.
2) The notarized documents should be authenticated (NOT apostilled) by the Departments of Foreign Affairs and Trade or its Office in States or Territories.
3) Apply for the documents authentication from the Chinese Embassy or relevant Consulate General where the documents notarized but not authenticated, in accordance with consular regions.