like yahoo mail did (new update as of october 2013),
i cant find library or script that can make a div transparent and at the same time blur.

and not like using two image, that one image is blur.

For the transparency, Read up on Opacity.
I achieve blur by giving the text within the elements which I want to blur a text shadow and no text colour (ie, no alpha in an rgba() set), for example:

.blurred
{
    color: rgba(0,0,0,0);
    text-shadow: 0px 0px 4px #000;
}

You could trigger this class to be applied to an element using Javascript.