wrote:

sorry, i change .bak to .dbx and use "Macallan Outlook Express
Extraction" tool ,"Recovery for Outlook Express" to restore, but i
cann't restore anything.

so would you like to give me a tool's name , so i can restore this
.bak file.

What application did you use to create this ".bak" file?

by the way, i am not true that the .bak file can rename to .dbx file,
because i see .bak is .pst's backup file.

Wrong. the file type .bak has no connection with Outlook at all. Most PST
backup file types are, well, ".pst".

but this .bak rename .pst ,
outlook and scanpst cann't not fix and input this file .

Probrbably because the file was neither a PST nor a DBX file to start with.
Instead, my guess is that it was created by some backup application (like
Microsoft Backup) that puts multiple files into a container file (the .bak
file in this case), the use of said application being required to extract
the files from the container. So, your next task is to use whatever
application you used to create the .bak file in the first place to restore
the original files contained in the .bak file. Only you know how you
created the .bak file. Only you can figure out how to restore it.
--
Brian Tillman