The asp.net achieve pop-up dialog box and display the chart

If I have understood you correctly, you need to show the chart in a popup with background theme masked (grayed out).

There are numerous way we follow depending upon the actual requirement,

1. Just place a div in the form with certain height and width. Position it relative and make it in centre. Make the display style to none.
On button click, populate the chart within the div and make it visible.
Use css to make the background theme masked.
(you can also use some animation effect of javascript or jquery to animate when open or close a div.

2. Use any JQuery overlay. This will make developer's lefe much easier.

Here is a link which will be helpful,
http://www.jquery-plugins.info/view.php?id=13732[^]

Hope this helps.
cheers