在调用 AdvancedSearch 方法时，使用 SearchScope 参数来指定搜索的范围。将它设置为 olSearchScopeAllFolders，可以搜索整个文件夹层次结构，包括子文件夹。以下是示例代码：

Sub SearchFolders()
    Dim objApp As Outlook.Application
    Dim objNS As Outlook.NameSpace
    Dim objFolder As Outlook.MAPIFolder
    Dim strSearch As String
    Dim objResults As Outlook.Results
    
    ' Set up Outlook objects
    Set objApp = CreateObject("Outlook.Application")
    Set objNS = objApp.GetNamespace("MAPI")
    Set objFolder = objNS.GetDefaultFolder(olFolderInbox)
    
    ' Set up search
    strSearch = "test"
    Set objResults = objFolder.AdvancedSearch(strSearch, "urn:schemas:mailheader:subject", olSearchScopeAllFolders)
    
    ' Display results
    If objResults.Count > 0 Then
        For i = 1 To objResults.Count
            MsgBox objResults.Item(i).Subject
        Next i
    Else
        MsgBox "No results found"
    End If
    
    ' Clean up
    Set objResults = Nothing
    Set objFolder = Nothing
    Set objNS = Nothing
    Set objApp = Nothing
End Sub