Thanks Guys for the trick. There is another one , just got to know from veritas 
 refernece.
If we specify the following option in vm.conf file , system will not eject the 
media after the backup .
DO_NOT_EJECT_STANDALONE

Other way as David mentioned , start ltid with -nsu flag also do the same 
function.
Malinda also suggest he following 
"Put a 0 kb file in the volmgr directory named NO_STANDALONE_UNLOAD with no 
file extension.  This will keep the tape from dismounting between backups."
Thanks again to all.
regards atif