I want to setup a site use Plone for my company for document management purpose. My company device in to 5 departments and only memper in this department can access the doccument. could you tell me how can I do? should I create 5 folder with user folder or create more 5 role and grand the member with their role?

In Plone, create 5 folders, keep all your users in the same user folder, and grant them local roles to the folderers they can access. In Zope, probably the multiple user folders is the way to go if nobody is supposed to exist in any of the other sibling folders. --jcc