I have a script that need to place after closing tag after of body?
Adding a &lt;script&gt; tag (or any tag except a comment) outside &lt;head&gt; or &lt;body&gt; is invalid HTML. Drupal doesn't want to help you to produce invalid HTML, so it contains nothing that would help you to do this.

I would examine your motivation for doing this, and reconsider whether you want to produce a valid or invalid document. If you really want to go down the invalid route, then you may as well just edit your theme's html.tpl.php file and stick the script at the bottom, as you won't find any API methods that can be used to do it for you.

FYI, IE10+ will ignore the script altogether, Chrome and FF will honour it for now, but may not in the future, other browsers/versions will probably do various other things.