thanks for your help
after more time of searching on internet i found out the sol. of the problem and then i advice any one want to join clear pass to domain
1- make sure of NTP with the domain host (time sync.)
2- find out the FQDN (server hostname.domain name.root name)
ex (hpserv.hp.com)
3-cheak your admin account privliges (can add machine to domain)
4- DNS of clearpass is the ip of the server domain