hi,,I am azad. from Bangladesh, please tell me about marriage in china for bangladeshi citizen.

Azad, you need to prepare your passport, residence permit or visa for PRC, and a single status certificate. If your fiancee is Chinese citizens, she needs to prepare her ID card, household registration book, as well as the single-status certificate. Then you two should go together to the local Civil Affairs Bureau to register the marriage.
Whether you are allowed to work is related to the type of your visa. If you have a Z type, then you can work. It's nothing to do with your marriage status.