• 用End定位最后一个数据行。
• 增加空白单的特殊处理代码。
• GoTo ImportData在你的代码中，但没有行号ImportData。
• 我建议避免使用GoTo。

Option Explicit

Sub ImportTXTFiles()
    Dim fso As Object
    Dim xlsheet As Worksheet
    Dim qt As QueryTable
    Dim txtfilesToOpen As Variant, txtfile As Variant
    
    Application.ScreenUpdating = False
    Set fso = CreateObject("Scripting.FileSystemObject")
    
    txtfilesToOpen = Application.GetOpenFilename(FileFilter:="Text Files (*.txt), *.txt", MultiSelect:=True, Title:="Text Files to Open")
    
    Dim oSht As Worksheet, sShtName As String
    For Each txtfile In txtfilesToOpen
        ' FINDS EXISTING WORKSHEET
        Set oSht = Nothing
        sShtName = Replace(fso.GetFileName(txtfile), ".txt", "")
        For Each xlsheet In ThisWorkbook.Worksheets
            If xlsheet.Name = sShtName Then
                Set oSht = xlsheet
            End If
        Next xlsheet
        If oSht Is Nothing Then
            MsgBox "Can't find sheet " & sShtName
        Else
            ' IMPORT DATA FROM TEXT FILE
            Dim c As Range
            With oSht
                Set c = .Cells(.Rows.Count, 1).End(xlUp).Row
                If c.Row > 1 Then
                    Set c = c.Offset(1, 0)
                ElseIf Len(c.Value) = 0 Then
                    Set c = c.Offset(1, 0)
                End If
            End If
            With oSht.QueryTables.Add(Connection:="TEXT;" & txtfile, Destination:=c)
                .TextFileParseType = xlDelimited
                .TextFileConsecutiveDelimiter = False
                .TextFileTabDelimiter = False
                .TextFileSemicolonDelimiter = False
                .TextFileCommaDelimiter = False
                .TextFileSpaceDelimiter = False
                .TextFileOtherDelimiter = "|"
                
                .Refresh BackgroundQuery:=False
            End With
            
            For Each qt In oSht.QueryTables
                qt.Delete
            Next qt
        End If
    Next txtfile
    
    Application.ScreenUpdating = True
    MsgBox "Successfully imported text files!", vbInformation, "SUCCESSFUL IMPORT"
    
    Set fso = Nothing
End Sub

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• Microsoft文档：*

Range.End property (Excel)