Is it possible to refer static resources files in formula fields

Unfortunately, it does not. The reason is that static resources cannot be referenced in formula fields.

But no big deal, because each static resource gets its own unique URL. So you could go to your static resource and click ‘Click here to view this file’ 
 
Refer:
http://improveit360.blogspot.in/2010/09/how-to-use-static-resource-images-in.html