you can apply for business visa which can be issued to aliens who come to China to attend exhibition. The below documents are required:
original Invitation Letter from the Canton Fair organizer.
Original Visa Notice Form issued by authorized departments of Chinese Government(the Canton Fair Organizor can apply for it for you, as I know, generally speaking, the Canton Fair only issue invitation letter, he won't apply for the visa notice form for you because appicants of UK, USA, Australia, Canada and EU members can easily get the business visa just by provide the invitation letter, however, for Bangladeshis, the Original Visa Notice Form issued by authorized departments of Chinese Government is required)
You can prepare the below documents by yourself:
1. Valid passport (at least six months before expiration) with blank visa pages and copy of the first three pages;

2. TYPED Visa Application Form with one passport photo.

3. Applicants who have never been to China before should submit in person.