After few hours of search i have found a easy solution and the right option to get memory size used by a process.
On Error Resume Next
Const wbemFlagReturnImmediately = &h10
Const wbemFlagForwardOnly = &h20
Dim sComputerName, sProcessName
sComputerName = "."
sProcessName = "explorer.exe"
Set objWMIService = GetObject("winmgmts:\\" & sComputerName & "\root\CIMV2")
Set colItems = objWMIService.ExecQuery("SELECT * FROM Win32_Process WHERE Name ='" & sProcessName & "'", "WQL",wbemFlagReturnImmediately + wbemFlagForwardOnly)
For Each objItem In colItems
WScript.Echo "-- Process --"
WScript.Echo "Caption : " & objItem.Caption
WScript.Echo "Name : " & objItem.Name
WScript.Echo "Mem usage : " & " - " & objItem.WorkingSetSize / 1024
Next