problem solved !!http://html5.litten.com/how-to-fix-external-disk-drive-suddenly-became-raw/
this link help me a lot.
the software can scan the historical partition tables in your disk.
then you can choose to restore the right partition (of course you need to press P to check whether the files inside are what you want or not.)
furthermore you can choose to copy a file, for example a movie, from those historical partitions to see if it can play.