I searched a lot for finding best space requirement algorithm for SATISFIABILITY problem but I didn't find any thing better than brute force that is in DSPACE(n). is there exists better bound? and what is best known bound.
If I understand your question correctly, as far as I understand this is computational-model dependent. An excellent lecture on the subject by Prof. Ryan O'Donnell can be found here: https://www.youtube.com/watch?v=_nCBH_lVjGU