<p>For e.g. if i am storing some files on a network server which is under many hierarchical folders.</p>

<p>Then i want to do backup. But i always encounter issue because the file path is more than 255?</p>

<p>How can i resolve this issue or work around it?</p>

Maybe upgrade to an Operating System that's been updated in the last decade or so? Seriously, though - what OS and file system are you using? Even FAT32 supports long path and file names, though any single component of the path is limited to 255 characters.
If you've got directories with more than 255 characters in their name, then that's problematic (and a little weird). To work around that issue, you could consider using an archiving utility (tar or zip) run on the server, then ship the archive over to yuor desktop machine.