Problems about spectral difference method
 

Is there anyone familiar with this method.
My question is how to transform a single physical element to a standard square one ?

I am not very familiar with the method but, if i understand your question, you should find relevant information in any serious book on the spectral element method, where quad/hexa elements are mapped from the physical space to the standard element.

I remember reading this stuff repeatedly in such books, but can't remember which one. Try:

1) Canuto, Hussaini, Quarteroni, Zang
2) Deville, Fischer, Mund
3) Karniadakis, Sherwin

I don't remember the titles but they all have "spectral element" inside.

Well, one of us is clearly thinking out of the box ;)