Dim spsite As New SPSite(ServerURL)
Dim spweb As SPWeb = spsite.OpenWeb()
Dim splist As SPList = spweb.Lists(ListName)
Dim MD5String As String = String.Empty
Dim foldername as string = "Category11"
spweb.AllowUnsafeUpdates = True
Dim Spitemfolders As SPListItemCollection = splist.Folders
Dim SPitemfolder As SPListItem
Dim isFolderNoExist As Boolean = True
For Each SPitemfolder In Spitemfolders
If SPitemfolder.Name = Foldername Then
isFolderNoExist = False
End If
Next
If isFolderNoExist Then
Dim newFolder As SPListItem = splist.Items.Add(splist.RootFolder.ServerRelativeUrl, PFileSystemObjectType.Folder, "")
newFolder("Name") = foldername
newFolder.Update()
endif