Hi Paul,
Thanks for your reply~ Changing the DB Host to FQDN do the trick.
Actually I also change the Ranger external url with FQDN, now it work great in Ambari 2.0.
For Detail:
Ambari > Ranger > Configs > DB setting > Ranger DB host , Setting this with FQDN.
Ambari > Ranger > Configs > Ranger Settings > External URL , Setting this with FQDN.