II have a list with lookup field .
I want created a chart with Chart WebPart that grouping data with lookup field and calculate sum a special field .
How can I do?
You can create your own webpart that inherits or contains a ChartWebPart. Then in code you can work with it getting by the fields, doing the calculations and adding the points to the chart.
Check the Microsoft.Office.Server.WebControls namespace in MSDN for details on how to programatically interact with the charts, add points, etc.