I need help for connecting Arduino Uno to C# GUI!!!!
You will need to provide more information that that.
use the Serial object on your arduino, and use the SerialPort class in C#
http://msdn.microsoft.com/en-us/library/system.io.ports.serialport(VS.90).aspx (http://msdn.microsoft.com/en-us/library/system.io.ports.serialport(VS.90).aspx)
The Python example in Reply #4 in this Thread (http://forum.arduino.cc/index.php?topic=225329.msg1810764#msg1810764) should give you the general idea.
...R