I understand your ans.But i want to know where is the stored truncate statement log.But in the redo log no entry for truncate.but i want to from which log it is reversing value..
If you are still asking after being given the answer then you don't 'understand'.
You were given the answer above. The flashback archive stores the data.
See the link that was provided above for CREATE FLASHBACK ARCHIVE in the SQL Language doc
Specify the tablespace where the archived data for this flashback data archive is to be stored. You can specify only one tablespace with this clause. However, you can subsequently add tablespaces to the flashback data archive with an ALTER FLASHBACK ARCHIVE statement.
The data is moved to the archive tablespace and restored from there when you do a flashback archive query.