Hi Lidong,
Did some research into Email Campaigns for you. Looking through the help files and running some tests, you can’t actually put a value directly into the email campaign. It is assumed that the Email campaign generally doesn’t cost enough per mailing to warrant a cost per view. To offset this, you can set up a Goal that represents the conversions of that email campaign. You would set the page of the Goal as being the same as the Email landing page. You would then set the number of hits or the dollar value you expect to hit for that page.
This will give you your ROI for the Email.
Brian