From the advice here I thought a plan.
we use windows 2003AD with 2008 server and we have some forestwide trust and we use MIIS for galsync.
1. make Temp site that has not included in any sitelink object.
2. move one least used DC(target DC) to Temp site.
3. prepare laptop PC that has Hyper-V(2008 or 2012)
4. Install windows2008 server as Hyper-V guest .
5. Promote Hyper-V guest windows2008 as DC in Temp site.
6. wait replication.
7. Take windows server backup of Hyper-V guest windows 2008.
8. Demote Hyper-V guest windows 2008.
9. move target DC to original site.
10. Disconnect laptop PC from network.
11. restore Hyper-V guest windows 2008 from windows server backup.
Does this make sence ?