我根据大家的回答，修改了一下代码，做到了重复选择就是取消选择的效果。可以试试。
Private Sub Worksheet_Change(ByVal Target As Range)
' Developed by Contextures Inc.
'
Dim rngDV As Range
Dim oldVal As String
Dim newVal As String
If Target.Count > 1 Then GoTo exitHandler
On Error Resume Next
Set rngDV = Cells.SpecialCells(xlCellTypeAllValidation)
On Error GoTo exitHandler
If rngDV Is Nothing Then GoTo exitHandler
If Intersect(Target, rngDV) Is Nothing Then
'do nothing
Else
Application.EnableEvents = False
newVal = Target.Value
Application.Undo
oldVal = Target.Value
Target.Value = newVal
If Target.Column = 7 Then '这里规定好哪一列的数据有效性是多选的，A列是第1列，依次类推，如3就是C列，7就是G列
If oldVal = "" Then
'do nothing
Else
If newVal = "" Then
'do nothing
Else
If InStr(1, oldVal, newVal) <> 0 Then '重复选择视同删除
If InStr(1, oldVal, newVal) + Len(newVal) - 1 = Len(oldVal) Then '最后一个选项重复
Target.Value = Left(oldVal, Len(oldVal) - Len(newVal) - 1)
Else
Target.Value = Replace(oldVal, newVal & ",", "") '不是最后一个选项重复的时候处理逗号
End If
Else '不是重复选项就视同增加选项
Target.Value = oldVal & "," & newVal
' NOTE: you can use a line break,
' instead of a comma
' Target.Value = oldVal _
' & Chr(10) & newVal
End If
End If
End If
End If
End If
exitHandler:
Application.EnableEvents = True
End Sub
