谢谢，  我后来在一本书上看到，用宏实现的。但是对A1这个单元格的计算，要是对（A1：A5）区域的计算，不知道怎么修改呢？
Dim i
Private Sub Worksheet_Change(ByVal Target As Range)
    If Target.Address = "$A$1" Then
        If Target.Value = "" Then
            Range("B1") = Range("B1") - i
        Else
            Range("B1") = Range("B1") + Target.Value
        End If
    End If
End Sub
Private Sub Worksheet_SelectionChange(ByVal Target As Range)
    If Target.Address = "$A$1" Then
        i = Target.Value
    End If
End Sub

Private Sub Worksheet_Change(ByVal T As Range)
    Application.EnableEvents = False
    If T.Column = 3 And T.Row >= 2 And T.Row <= 13 Then
        T.Offset(0, 2) = T.Offset(0, 2) + T
    End If
    Application.EnableEvents = True
End Sub