Cloud   computing   is   one   of   today’s   most exciting technology because of its cost-reducing, flexibility, and  scalability.  With  the  fast  growing  of  cloud  computing technology,   Data   security   becomes    more   and    more important  in  it.  In  evaluating  whether  to  move  to  cloud computing,  it  is  important  to  compare  benefits  and  also risks  of  it.  Thus,  security  and  other  existed  issues  in  the cloud  cause  cloud  clients  need  more  time  to  think  about moving  to  cloud  environments.  But  Security-related  topics is  one  of  the  most  arguable  issues  in  the  cloud  computing which  caused  several  enterprises  looks  to  this  technology uncertainly  and  move  toward  it  warily.  Virtualization  is  a term  that  refers  to  the  abstraction  of  computer  resources. The   purpose   of   virtual   computing   environment   is   to improve   resource   utilization   by   providing   a   unified integrated  operating  platform  for  users  and  applications based  on  aggregation  of  heterogeneous  and  autonomous resources. More recently, virtualization at all levels (system storage, and  network) became important again as a  way to improve system security, reliability and availability, reduce costs and provide greater flexibility