好的，让@stucharo的算法有点简单一些。

OK, let's have the algorithm from @stucharo a little bit simpler to extend.

Public Function getHTMLFormattedString(r As Range) As String

 isBold = False
 isItalic = False
 isUnderlined = False
 s = ""
 cCount = 0
 On Error Resume Next
 cCount = r.Characters.Count
 On Error GoTo 0

 If cCount > 0 Then

  For i = 1 To cCount

   Set c = r.Characters(i, 1)

   If isUnderlined And c.Font.Underline = xlUnderlineStyleNone Then
    isUnderlined = False
    s = s & "</u>"
   End If

   If isItalic And Not c.Font.Italic Then
    isItalic = False
    s = s & "</i>"
   End If

   If isBold And Not c.Font.Bold Then
    isBold = False
    s = s & "</b>"
   End If


   If c.Font.Bold And Not isBold Then
    isBold = True
    s = s + "<b>"
   End If

   If c.Font.Italic And Not isItalic Then
    isItalic = True
    s = s + "<i>"
   End If

   If Not (c.Font.Underline = xlUnderlineStyleNone) And Not isUnderlined Then
    isUnderlined = True
    s = s + "<u>"
   End If

   s = s & c.Text

   If i = cCount Then
    If isUnderlined Then s = s & "</u>"
    If isItalic Then s = s & "</i>"
    If isBold Then s = s & "</b>"
   End If

  Next i

 Else
  s = r.Text
  If r.Font.Bold Then s = "<b>" & s & "</b>"
  If r.Font.Italic Then s = "<i>" & s & "</i>"
  If Not (r.Font.Underline = xlUnderlineStyleNone) Then s = "<u>" & s & "</u>"
 End If

 getHTMLFormattedString = s
End Function

要清楚，此功能仅适用于包含单个单元格的范围。但是，对于每个单元格来说，这个函数应该在更大的范围内调用，并将返回的字符串连接成一个。

To be clear, this function works only with a range containing a single cell. But it should be easy calling this function for each cell in a bigger range and concatenating the returned strings into one.

由OP编辑：

我通过以下代码调用函数：

I called the function by the below code:

Sub ReplaceFormattingTags()

Dim i As Integer, j As Integer
Dim rng As Range
Dim Txt As String

Set rng = Range("A2:C15")
For i = 1 To rng.Rows.Count
    For j = 1 To rng.Columns.Count
        Txt = Txt & getHTMLFormattedString(rng(i, j)) & " "
    Next j
    Txt = Txt & vbCrLf
Next i

Debug.Print Txt

End Sub