I have a code that wrote with C#.But I need to convert it to VBA and then use from it into GIS. how can I convert it be VBA?
It really depends on how much code you are talking about. Most people try to go the other way, that is VB6\VBA to c# or vb.net.
But for your case a start might be to convert the methods to VB.net and then clean up the code to VBA.