Step or Solutions to Install client agent on HP-Alpha Tru64 V5.1B

No idea why you are saying 'after patch agent can not run.'

You will need these base 6.5 installations:

NetBackup Unix Client1 (Tru64(Alpha), HP's and AIX)

NetBackup Unix Options/Database Agents

Plus 6.5.6 patches from http://www.symantec.com/docs/TECH129076 :

NB_CLT_6.5.6.tar provides updates for NetBackup 6.5 for all UNIX clients. 
  http://www.symantec.com/docs/TECH129328 

NB_JAV_6.5.6.tar provides an update to NetBackup 6.5 Java on UNIX platforms
  http://www.symantec.com/docs/TECH129333

NB_ORA_6.5.6.tar provides updates to NetBackup 6.5 for Oracle Database Agent on UNIX platforms
  http://www.symantec.com/docs/TECH129343

Thanks, Marianne. Now I can install HP agent V.6.5 on this machine, but! can not patch to 6.5.6.(after patch agent can not run.) And can not install option database agent. (it's Require 6.5.6 patch) I recommend the customer for backup&restore as a file level. Best regards.

Support from HP for True64 has ended long time ago (http://h30097.www3.hp.com/pdf/Tru64_Roadmap_Current.pdf ) 
If I am not mistaken Oracle support for version 9 has also ended...

You will therefore understand that Symantec can no longer support this OS.

NBU 7 OS CL: http://www.symantec.com/docs/TECH76648

NBU 6.5 was the last version to support True64: http://www.symantec.com/docs/TECH70729 

So, the only way to back this up is to find NBU 6.5 installation media. 
This version is no longer available on FileConnect as support ended in Oct 2012.
If you do not have a set of download files or original dvd's, your only hope is to find a Symantec partner or SE with a set of dvd's in a 'bottom drawer'.

Best to convince system owners and dba's to move to supported OS and database versions.