how can get Chinese visa for businss purpose without authenticated invitation letter?

For Bangladeshi applicants, you have to get an Invitation Letter of Duly Authorized Unit or Confirmation Letter of Invitation(Invitation Letter of Duly Authorized Unit and Confirmation Letter of Invitation refer to the documents issued by the Chinese government department’ companies and social organizations authorized by the Chinese Foreign Ministry, such as Foreign Affairs Office, Bureau of Foreign Trade and Economic Cooperation.

Without it, you can't get a business visa. The invitation letter doesn't need to be authenticated.