sir i am a indian passport holder,residing in guangzhoz since 17 years,how do i get bangladesh visa

If you go there for tourism purpose, you can apply for a tourist entry permit. The first step is to prepare the relevant materials including the application form, 2 passport-style photos, your passport, financial support, proof and flight tickets, and other documents required by the consular officers.
Next step is to hand in the application to the embassy of Bangladesh in Beijing to apply for it.