我认为登录页面在之后无法立即使用 WebBrowser1.Navigate .尝试将 DocumentComplete 处理程序添加到 WebBrowser1 ，然后将处理登录页面的相应代码移至此处(当前位于 Navigate 行).使用调试器检查行为.

I think that the login page is not available immediately after WebBrowser1.Navigate. Try adding a DocumentComplete handler to WebBrowser1 and move here the corresponding code that processes the login page (which currently is after Navigate line). Check the behaviour with debugger.