参考下面的代码

Dim r As Row = Tables("表A").rows(2)

Dim s1() As String = "3,4,5".Split(",")
Dim s2() As String = r("第二列").split(",")
Dim nstr As String = r("第二列")
For Each s As String In s1
    If array.indexof(s2, s) = -1 Then
        nstr &= "," & s
    End If
Next

msgbox(nstr.trim(","))

 For Each dr As DataRow In DataTables("表A").dataRows
    Dim ls As new List(Of String)
    For Each s As String In dr("第二列").split(",")
        If ls.Contains(s) = False Then
            ls.Add(s)
        End If
    Next
    dr("第二列") = String.Join(",", ls.ToArray)
Next