I am bangladeshi by birth.i live in Italy almost six years.and i have italian stay permission.now can i apply?

To obtain Italian Citizenship, there are several ways:

1. Italian ascendancy( ancestry) , you being the most recent descendant.
2. Marriage to a citizen of Italy followed by two years residency.
3. 10 years residency in Italy if you are not an EU citizen &/or you are a citizen of a non EU country.

So in your case being from Bangladesh, the requirement is another 4 years residency making a total of 10 years before you can apply for Italian citizenship.

No you can't apply for an Italian passport, ONLY Italian citizens can apply for those.......... what you mean by 'italian stay permission' is anyone guess so I suggest you look on Italy's immigration website and chech what visa you have and if it has any rights after x number of years of legally living/working there for you to start the process of citizenship

Why are you asking this in english in the australian answers?