[PROBLEM] How to recover the database files by pi/moodeaudio, without the password of root?

[vinnn]

Transfer files to pi's home directory as the pi user
SSH into your Pi and mv the files as the root user using sudo, e.g.

Code:

sudo mv somefile /some/destination

It they're mpd files you'll also need to change ownership back to the mpd user, e.g...

Code:

sudo chown -R mpd:audio /var/lib/mpd

Thanks, Vinnn.

You mean I should upload the files into pi's folder at first, and

Code:

sudo mv database /var/lib/mpd/database -f

sudo mv libcache.json /var/local/www/libcache.json -f

sudo chown -R mpd:audio /var/lib/mpd

Correct?

Yes but you don't need the -f option and you put it in the wrong place anyway.
Command options generally go after the command, not after the arguments.