when I used the serveradmin to watch the System log.
I saw the error message log :
Apr 28 00:30:07 macminiserver org.clamav.clamd[11273]: LibClamAV Warning: **************************************************
Apr 28 00:30:07 macminiserver org.clamav.clamd[11273]: LibClamAV Warning: *** The virus database is older than 7 days! ***
Apr 28 00:30:07 macminiserver org.clamav.clamd[11273]: LibClamAV Warning: *** Please update it as soon as possible. ***
Apr 28 00:30:07 macminiserver org.clamav.clamd[11273]: LibClamAV Warning: **************************************************
Apr 28 00:30:07 macminiserver org.clamav.clamd[11273]: LibClamAV Error: cli_loadinfo: Digital signature not found
Apr 28 00:30:07 macminiserver org.clamav.clamd[11273]: LibClamAV Error: Can't load daily.info: Malformed database
Apr 28 00:30:07 macminiserver org.clamav.clamd[11273]: LibClamAV Error: cli_tgzload: Can't load daily.info
Apr 28 00:30:07 macminiserver org.clamav.clamd[11273]: LibClamAV Error: Can't load /var/clamav/daily.cvd: Malformed database
Apr 28 00:30:07 macminiserver org.clamav.clamd[11273]: ERROR: Malformed database
Apr 28 00:30:07 macminiserver com.apple.launchd[1] (org.clamav.clamd[11273]): Exited with exit code: 1
Apr 28 00:30:07 macminiserver com.apple.launchd[1] (org.clamav.clamd): Throttling respawn: Will start in 10 seconds
then I restart my clamav freshclam and update clamav
#sudo launchctl unload -w /System/Library/LaunchDaemons/org.clamav.freshclam.plist
#sudo launchctl load -w /System/Library/LaunchDaemons/org.clamav.freshclam.plist
after this command, we can check the log in the serveradmin and it will start to update the virus database. And the error log does not appear again.