As u saw the top screenshot which I attached, there have two pixel between drop menu and the nav menu, how can I let the drop down menu parallel to the bottom of the nav menu? thx in advance.

Can you supply a link to the site?

Hi lmilesw, here you go. http://virovek.labiology.com/

Actually I think it's only a 1px drop. I hardly noticed it but the following should "fix" it.

.rMenu-expand li {
    position: relative;
    top: 1px;
}