Thanks Ed and Voide,
@Voide: You are right, I found one SP which seems to be culprit, its runnig from long time , but not blocking anything. Might it is using much space in Tempdb. Attached is the SP. I am not good at creating\editing SP. So if anyone find anything wrong in this SP pls let me know so that I can suggest my customer to edit that SP so it will not use so much space in TempDB.
@Ed: First of all Thanks for your valuable suggestion, I know it that restarting services will refresh the tempdb but each time restarting services is not proper and permanat solution. Thats why I want to know the root cause to TempDb's space eating.