check below mention Script.....
Const JOIN_DOMAIN = 1
Const ACCT_CREATE = 2
Const ACCT_DELETE = 4
Const WIN9X_UPGRADE = 16
Const DOMAIN_JOIN_IF_JOINED = 32
Const JOIN_UNSECURE = 64
Const MACHINE_PASSWORD_PASSED = 128
Const DEFERRED_SPN_SET = 256
Const INSTALL_INVOCATION = 262144
strDomain = "domain name"
strPassword = "password"
strUser = "fmdesktopadmin"
Set objNetwork = CreateObject("WScript.Network")
strComputer = objNetwork.ComputerName
wscript.echo strcomputer
Set objComputer = GetObject("winmgmts:{impersonationLevel=Impersonate}!\\" & strComputer & "\root\cimv2:Win32_ComputerSystem.Name='" & strComputer & "'")
ReturnValue = objComputer.JoinDomainOrWorkGroup(strDomain,strPassword, strDomain & "\" & strUser, NULL,JOIN_DOMAIN + ACCT_CREATE)