Thanks ,but it did not work out as separate delete

-- separate delete works fine

--Remove all the diff backups from delete cmd

Delete from #ExistingBackups where Name like '%_diff%'

--Remove all the Tran backupsfrom delete cmd

Delete from #ExistingBackups where Name like '%.trn'

--Remove all the files that dont have Date stamp from delete cmd

Delete from #ExistingBackups where ISNUMERIC(Right(SUBSTRING(name,1,charindex('.',name)-1),8))=0

--Remove sys databases from delete cmd

Delete from #ExistingBackups where Name like '%master%' or Name like '%model%' or Name like '%msdb%'

--Remove all the files that are greater than threshold from delete cmd

Delete from #ExistingBackups where Right(SUBSTRING(name,1,charindex('.',name)-1),8) > @LastBackupToKeep

--************************************************************************

--Does not work as above

delete from #ExistingBackups

where

(Name not like '%master%' and Name not like '%model%' and Name not like '%msdb%') or

(ISNUMERIC(Right(SUBSTRING(name,1,charindex('.',name)-1),8))=0) or

(Right(SUBSTRING(name,1,charindex('.',name)-1),8) > GETDATE()-1) or

(Name like '%.trn')or

(Name like '%_diff%')