For Each elem As HtmlElement In wb1.Document.GetElementsByTagName("button")
    ' Check the attributtes you want
    If elem.GetAttribute("class") = "btn btn-default" Then
        'Check even the text if you want
        If elem.InnerText = "Login" Then
            'Invoke your event
            elem.InvokeMember("click")
        End If
    End If
Next

这将搜索文档上的所有按钮元素.您可以通过查看包含具有ID或其他内容的按钮的元素来缩小搜索范围：

Dim myElem As HtmlElement = wb1.Document.GetElementById("myContainerId")
For Each elem As HtmlElement In myElem.GetElementsByTagName("button")
    '...
Next