1. you need to present your original Employment License for Foreigners issued by Ministry of Human Resources and Social Security of China and copy; original Visa Notice Form issued by authorized departments of Chinese Government; Physical Examination Report from local public hospitals and copy; your marriage certificate; You wife's valid passport (at least six months before expiration) with blank visa pages and copy of the first three pages; TYPED Visa Application Form with one passport photo.
2. you can post all the documents to your wife and ask her to apply for the visa from the China embassy in Bangladesh.
3. There is no need to change the passport, if it is a valid passport (at least six months before expiration) with blank visa pages and copy of the first three pages.