Do I need any invitation leter if I want to apply visa for Macaw ?

First, you don't need an invitation letter from Macau side. You can submit the requirements to Embassy and Consulate of the People's Republic of China or Immigration Department of Macau SAR Government to aply for the visa. The requirements are listed on this page: https://www.travelchinaguide.com/embassy/visa/macau.htm

i am a bangldeshi citizen and want to visit macaw as a tourist. i do not know any body or any company in macacw.how i can get visa for macaw then?

You can contact a travel agency to issue you Tour receipt, itinerary, you don't need the invitation letter from somebody or a company if you come to Macau as a tourist.